Our understanding on how dislocation textures quantitatively affect thermal conductivity has been limited. We investigate the impact of kink dislocations on phonon thermal conduction in MgO by molecular dynamics, through changing edge and screw components in kink dislocations. The thermal conductivity is almost independent of the length of the edge component, but is rather reduced significantly with increasing the length of screw component, resulting in lower thermal conductivity than perfect edge dislocations. This reveals the combined effect of the edge and screw components on thermal conductivity beyond the simple description as one-dimensional obstacles and linear elastic strain field. Atomic contributions to thermal conductivity show that not only atoms in the vicinity of the kink dislocation cores but also those away from the cores exhibit suppressed thermal conductivity compared to the perfect edge dislocations. These results indicate that it is possible to efficiently reduce thermal conductivity in complex dislocation textures in real materials.

The development of a high-speed sintering method that can shorten the entire sintering time while guaranteeing the mechanical properties is very attractive as a sintering process for structural ceramic polycrystals. For this purpose, a sintering protocol that combines shrinkage-rate-controlled flash sintering, which controls the shrinkage rate to be constant with the use of an alternative current electric field, and a rapid furnace ramp were applied to 3-mol % Y₂O₃-doped ZrO₂ (3YSZ). As a result, a 3YSZ sintered polycrystal with about the relative density of 99.5 % (6.06 g/cm³) could be successfully fabricated within 30 min as the entire sintering time, which includes the furnace-heating regime. The sintered 3YSZ polycrystal is confirmed to exhibit a Vickers hardness of approximately 1290 HV and a fracture toughness (K_IC) of approximately 5.2 MPa m^1/2, which are similar values to those obtained from a typical thermally sintered 3YSZ polycrystal.

The effect of different annealing atmospheres on the atomic structures and dopant segregation behaviors in Ti-doped grain boundaries (GBs) of alumina was studied by using atomic-resolution scanning transmission electron microscopy, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy. In addition to the Ti dopants, Ca impurities also segregated to the GBs. It is found that the atomic structure of Ti-doped GBs is symmetric in the reducing atmosphere, while it changes into an asymmetric one with further annealing in air. The different GB structures and segregation behaviors of Ti and Ca in air may result from the partially oxidization of Ti³⁺ to Ti⁴⁺ and less oxygen vacancies when annealed in air. Our results indicate that the annealing atmosphere strongly affect GB segregation behaviors in alumina.

II–VI semiconductors, including Cd compounds, become brittle under light illumination. This phenomenon is known as the photoplastic effect (PPE) and is thought to arise from interactions between glide dislocations and photoexcited carriers. The present study investigated atomic structures of 30° Shockley-partial dislocations with and without excess carriers in CdX (X = S, Se and Te), by density-functional-theory (DFT) calculations. It was found that both Cd and anion cores favor unreconstructed atomic structures when excess carriers are absent. In the presence of excess carriers, on the other hand, reconstructed atomic structures were more stable at the anion cores while the unreconstructed ones were still energetically more favorable at the Cd cores. It is thus expected that only the anion cores change their atomic structures by light illumination, which can retard glide-dislocation motion by forming like-atom bonds. Analyses of local densities of states (LDOSs) revealed that the reconstructed Cd and anion cores form shallow and deep defect states within the band gaps, respectively. This determines the possible atomic reconstructions at the dislocation cores in the presence of excess carriers excited by external light.

Adding carbon nanotubes (CNTs) into ceramics is an important way to promote toughness. Crystalline defects existing in materials play a significant role in affecting both their mechanical and functional performances because they bring symmetry breaking of the periodic lattice structures. For CNTs existing in real ceramic materials, which almost appear as polycrystalline forms, the most notable defects are the grain boundaries (GBs) which consist of defect cores of dislocations. It is of engineering importance to investigate the effects of these defect cores of GBs on the strength of the polycrystalline CNTs to promote the composites’ performances. The variety of grain orientations of the polycrystalline CNTs allows the GBs to have various misorientations and different arrangements of the defect cores of dislocations at the GBs, which causes disparity in the stress fields near the GBs under an external stress condition, thus making distinguishable effects on the strength. While effective rules have been established for graphene (GP) GBs to predict the tensile strengths of GP GBs with different misorientations, the effects of misorientation and curvature on the strength of CNT GBs have yet to be reported. This work studied these effects by molecular dynamics (MD) simulation. The results illustrate that the misorientation and temperature have much more significant effects than the curvature on the strength of CNT GBs, and verified a consistent tendency of the misorientation-strength relationship of the CNT GBs with the corresponding GP GBs. The CNT GBs and their corresponding GP GBs have almost identical strengths for most of the simulated results. Notable differences between CNT and GP GBs were only found at misorientations near 0 and 30° in armchair GBs. These strength differences were attributed to the crack stabilization and structural reconstruction in CNT GBs.

The photoplastic effect, phenomena that flow stress and/or hardness change by light illuminations, has been known mainly in II–VI compound semiconductors. In this study, it was revealed for the first time that magnesium oxide (MgO) single crystals exhibit increase in flow stress by light illumination, namely, the positive photoplastic effect. Scanning transmission electron microscope (STEM) observations demonstrated that the plastic deformation of MgO is realized by generation of glide dislocations on the slip system of {110}〈110〉. Therefore, the observed positive photoplastic effect of MgO is likely due to interactions of the glide dislocations and photo-excited carriers. According to the theoretical calculations, individual dislocations in MgO had a specific band structure that differs from the bulk. This also indicates possible interactions between dislocations and carriers. It is expected that light illumination can reduce dislocation mobility in MgO, leading to the increase in flow stress under light illuminations.

Mass transfer along a grain boundary (GB) in a Σ31 alumina bicrystal wafer was investigated using the oxygen permeation technique with ¹⁸O₂ at 1873 K, where oxide ions migrated along the GB from the high oxygen partial pressure [P_O2(hi)] surface to the low oxygen partial pressure [P_O2(lo)] surface, and aluminum ions moved concurrently in the opposite direction. It was found that the application of an oxygen potential gradient more strongly inhibited the migration of oxide ions along the GB within a shorter distance from the P_O2(hi) surface, compared with the case of the polycrystalline alumina. Moreover, in the case of high-angle GBs like Σ31 GB, as the GB gets close to the surface, the GB plane undergoes more pronounced lateral movement in the transverse direction. The GB movement is thought to be due to annihilation of aluminum vacancies stagnating in a nonequilibrium state near the surface.

Tin dioxide (SnO₂) is a semiconductor with significant potential for use in the electronic industry, including sensors, transparent electrodes, and thin film transistors among other purposes. To realize these applications, the synthesis of high-quality thin films is a prerequisite. Here, we show the epitaxial growth of SnO₂ films on (1−100) α-Al₂O₃ (M-sapphire) by pulsed laser deposition method. The epitaxial relationship was clarified to be (001)[100]SnO₂ || (1−100)[0001] α-Al₂O₃ with 4-fold symmetry, consistent with that grown on (001) TiO₂ single crystal. Orthorhombic distortion was absent, possibly owing to a combination of high strain relaxation due to a large lattice mismatch along [0001] α-Al₂O₃, coupled with a negligible mismatch-induced strain absence along [11−20] α-Al₂O₃. The mobility increases up to ∼57 cm² V⁻¹ s⁻¹ with increasing film thickness while the density of states (DOS) effective mass keeps a constant around the theoretical value of ∼0.3 m₀. Furthermore, the trend of carrier concentration versus mobility is analogous to those of single crystal SnO₂, thereby indicating the applicability of M-sapphire substrates in facilitating the epitaxial growth of high-quality SnO₂ films.

The surface image measurement time was reduced by data completion using a compressed sensing algorithm in the image-acquisition of scanning probe microscopy. In particular, by reducing the number of acquisition points of the surface-roughness image and reconstructing the image using estimated values, acquiring the surface image at one-eighth of the data-measurement time became possible. The reduced measurement time was shown to reduce the influence of thermal drift during image capture. The real time surface image demonstrated that reconstruction is possible during surface image acquisition.

The reaction distribution in the composite cathode of an all-solid-state battery (ASSB) was directly tracked by in situ scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX). Contact between an electrode active material and a solid electrolyte is important for improving the properties of ASSBs as a promising next-generation battery. An in situ analysis is significant for establishing strategies to obtain sufficient contact areas between the active material and solid electrolyte particles. SEM-EDX has the advantages of in-situ measurement in spatial/time resolution, non-destruction, and versatility. We investigated the sensitivity of EDX to the Na signal and distinguishable distance to ensure sufficient spatial/time resolution. The acceleration voltage of 5 kV for the electron beam provided the highest sensitivity to the Na signal among all acceleration voltages. The distinguishable distance decreased with increasing magnification owing to the decrease in pixel size. Cross-sectional SEM-EDX images of the TiS₂–Na₃PS₄/Na₃PS₄/Na–Sn cell were collected during charge/discharge. The time variation of Na signal intensity confirms the deintercalation of Na⁺ in the TiS₂–Na₃PS₄ cathode layer. Moreover, intercalation on the solid electrolyte side proceeded faster than that on the current collector side. This was because the rate-determining step was ionic conductivity rather than electronic conductivity based on the difference between ionic and electronic conductivities. Ex situ observations detected only a uniform distribution in the composite after Na⁺ diffusion had relaxed. Operando SEM-EDX is a new tool to directly explore the intermediate conditions of electrode materials under ASSB operation.

Mobility of dislocations in compound semiconductor materials can be changed by light illumination because the core structure of dislocations is supposed to be reconstructed by photoexcited carriers. However, the atomic structure of such dislocation cores has not been observed and is still poorly understood. In this study, we introduced dislocations in ZnS, one of the typical II–VI type compound semiconductors, by deformation under darkness, and investigated the atomic structure of the dislocation cores using scanning transmission electron microscopy (STEM) combined with theoretical calculations. Direct observation of the Zn core partial dislocation revealed that its atomic structure is in good agreement with the theoretically predicted dislocation core without electron trapping. Moreover, the dislocations were observed to move along a slip plane during the observation. These results indicate that the electron-trap-free dislocation is mobile and could be the origin of plasticity in the dark.

Scanning tunneling microscopy imaging of Fe deposited SrTiO₃(100)-(√13 × √13)-R33.7° surface is presented. Low-energy electron diffraction patterns showed that the surface reconstruction remained after Fe deposition at room temperature. Fe deposition generated defects, including oxygen vacancies, on the SrTiO₃(100)-(√13 × √13)-R33.7° surface. These defects have a periodicity with the c(√13 × √13) symmetry. Scanning tunneling spectroscopy demonstrated the formation of two types of defects: one had the same density of state with defects on the bare SrTiO₃(100)-(√13 × √13)-R33.7° surface, and the other had a narrow band gap structure. These results are attributed the formation of a two-dimensional hole gas at the FeO_x/SrTiO₃(100) interface.

We have prepared a dense ceramic sample of a novel thermoelectric sulfide Ta₂PdS₆ by means of spark plasma sintering technique under a uniaxial pressure. The Rietveld analyses of the X-ray diffraction patterns have clarified occurrence of weak preferred orientation in the sintering process. Resistivity, thermopower, and Hall resistivity measurements on the ceramic sample have indicated that it shows higher carrier density and lower carrier mobility than a single crystal. The inferior carrier mobility in the ceramic sample may partly come from increased point-defect and/or grain-boundary scattering, to which poor power factor is attributed.

Sulfide-type solid electrolytes for all-solid-state lithium-ion batteries are required to have high ionic conductivity, high (electro) chemical stability, and suitable mechanical properties. Compositing different materials is widely performed in developing multifunctional materials. However, only a few studies have investigated sulfide electrolytes due to the concern of lowering ionic conductivity. In this study, composite electrolytes comprising Li₁₀GeP₂S₁₂ (LGPS)-type electrolytes and nanosized Al₂O₃ are fabricated by a solid-state reaction. Al₂O₃ particles are mainly located in the voids between LGPS particles, whereas very limited oxygen content is substituted for sulfur in the LGPS structure. LGPS–Al₂O₃ composites exhibit ionic conductivities of ∼5 mS cm⁻¹ without significant changes by compositing Al₂O₃. LGPS–Al₂O₃ composites are softer and have higher atmospheric stability than uncomposed LGPS. All solid-state cells that use air-exposed LGPS–Al₂O₃ as a separator layer exhibit an improved cycle retention compared with that using air-exposed LGPS. These results demonstrate that electrolyte compositing is an effective means of improving other properties while maintaining high lithium ionic conductivity.

The structural and mechanical reliability of inorganic semiconductors for practical applications is determined by the rate at which they can deform and sustain externally applied strain. In this research, nanoindentation experiments under three strain rates and two light conditions were performed on single-crystal ZnS with an 80 nm radius Berkovich tip at a peak load of 60 µN. Significant pop-in events were observed in all indentation tests. The calculated maximum resolved shear stress at the first pop-in approximated the theoretical strength of ZnS, indicating a homogeneous dislocation nucleation process. The cumulative spreads of the maximum shear stress were found to be insensitive to the strain rate, and the distribution at a small strain rate was slightly broader than that of the other two strain rates because of thermal noise. Calculated activation energy ΔG required for the dislocation nucleation indicates that dislocation nucleation in ZnS could occur with external stress and without much assistance of thermal energy, leading to weak dependence of the first pop-in on the strain rate. At three strain rates, light consistently showed little influence on the pop-in behavior and dislocation nucleation process.

Li ionic conductors that are stable to lithium metal with high ionic conductivity are required as solid electrolytes for all-solid-state lithium metal batteries with high energy density. Lithium dendrite growth leading to short-circuit is one of the major issues to solve for developing practical batteries using lithium metal electrodes. We have introduced Li₃PO₄ (LPO) and Li₃BO₃ (LBO) as a grain boundary phase in the garnet-type lithium ionic conductor, Li_6.25Ga_0.25La₃Zr₂O₁₂ (LGLZ), by co-sintering. The lattice parameters, sinterability, elemental distribution, particle morphology, and electrochemical properties have been investigated. The sinterability has decreased with the introduction of LPO and LBO, while no significant change in the ionic conductivity is observed. The LGLZ with LPO was unstable to Li metal and did not exhibit the improvement of Li plating/stripping. Meanwhile, the LBO introduction into the grain boundary as a functional core increased the critical current density of the short circuit. Li dendrite growth could be suppressed by modifying the grain boundaries of the sintered body.

Ga- and Gd-substituted garnet-type Y₃Al₅O₁₂:Mn⁴⁺ phosphors, Y₃(Al_1−xGa_x)₅O₁₂:Mn⁴⁺ and (Y_1−yGd_y)₃Al₅O₁₂:Mn⁴⁺, were synthesized by a conventional solid-state reaction to elucidate the relationship between the emission and the local structure of the activator in the host material. Completely substituted Y₃(Al_1−xGa_x)₅O₁₂ and ∼80 % substituted (Y_1−yGd_y)₃Al₅O₁₂ (y ≤ ∼0.8) solid solutions have been produced. The lattice parameters of the garnet-type solid solutions increased linearly with the substitution of Ga and Gd for Al and Y sites, respectively. The emission peak attributed to the Mn⁴⁺ luminescence center of their garnet-type solid solutions shifted toward a longer wavelength side by substituting Ga and Gd. The emission peak wavelength of the Mn⁴⁺-activated garnet-type solid solutions increased almost linearly with increasing the average bond length between the cation and anion in the dodecahedral sites. The dodecahedral site in the garnet structure is edge-sharing with the octahedral site where Mn⁴⁺ exists. These results indicate that the emission wavelength can be controlled by changing the local structure around Mn⁴⁺ due to the cation substitution of coordination polyhedra neighboring Mn⁴⁺ coordination polyhedra.

Octacalcium phosphate (OCP) has a layered structure and various carboxylate ions can be incorporated into its structure as interlayer ions. In recent studies, aromatic carboxylate ions have been incorporated into OCP to impart fluorescence properties. In such fluorescent OCP materials, the incorporated carboxylate ions can be regarded as ‘crystal defect cores’. Although fluorescent OCPs with incorporated benzenedicarboxylate ions have been reported, the synthesis and fluorescence of OCPs with incorporated pyridinedicarboxlate ions have not yet been investigated. In this study, our aim was to synthesise OCP with incorporated 2,5-pyridinedicarboxylate ions and evaluate its fluorescence behaviour. Samples were synthesised by reacting calcium carbonate and phosphoric acid in 2,5-pyridinedicarboxylic acid solution. When the 2,5-pyridinedicarboxylic acid concentration in the solution was low, plate-shaped crystals of OCP with incorporated 2,5-pyridinedicarboxylate ions were formed. As the 2,5-pyridinedicarboxylic acid concentration increased, OCP formation was suppressed, and a poorly soluble salt composed of calcium and 2,5-pyridinedicarboxylate ions was formed in its place. The (100) interplanar spacing of OCP was increased from 1.87 to 2.26 nm by the incorporation of 2,5-pyridinedicarboxylate ions as interlayer ions. The incorporation of 2,5-pyridinedicarboxylate ions was confirmed by Fourier-transform infrared spectroscopy. OCP with incorporated 2,5-pyridinedicarboxylate ions exhibited fluorescence with an emission wavelength of 430 nm upon excitation at 320 nm. The results of this study should prove useful for the design and development of fluorescent OCP materials.

Alkaline earth (AE) metal-alloyed SnS films with a bandgap of 1.8 eV were demonstrated to us promising for their use in widegap photovoltaic absorbers by forming a p-n junction with an n-type CdS layer. The Ba-alloyed-SnS film exhibited the highest efficiency among the three types of AE-alloyed SnS films (barium, calcium, and strontium alloyed-SnS films). Electricity generation by the formation of the junction of p-AE-alloyed SnS/n-CdS indicates the possibility of realizing Si-based tandem solar cells.

Ti_1−2x(FeNb)_xO₂ solid solutions were prepared as visible-light-active photocatalysts using a conventional solid-state reaction method. Ti_1−2x(FeNb)_xO₂ solid solutions were obtained below x = 0.25 without any secondary phase. They exhibited light absorption in the visible region. The strong absorption corresponding to the bandgap shifted to the lower energies with increasing x. Because the valence band maxima of the samples remained unchanged, the conduction band minima shifted to lower energies. The photocatalytic activity was evaluated based on the degradation of methylene blue under UV–visible light irradiation. The photocatalytic activity of Ti_1−2x(FeNb)_xO₂ solid solutions tends to improve with increasing x. Clear visible light photocatalytic activity corresponding to the band gap was also observed. Thus, these materials are promising candidates for environmental applications.

In this study, high-sulfur-containing carbon replica (sulfur-rich S-CR) composites were prepared using a melt-diffusion method. Melt diffusion under vacuum enabled the introduction of four times the weight ratio of sulfur into the mesopores of a carbon replica (CR). The obtained sulfur-rich S-CR exhibited an initial discharge capacity of 700 mAh g_sulfur⁻¹, indicating the low utilization of sulfur in the composite. The classification of the particle sizes of the solid electrolyte and CR contributed to the improvement in electrochemical performance. An initial discharge capacity of over 1,200 mAh g⁻¹ was confirmed for the S-CR composite using the smaller solid electrolyte and CR prepared via a dry classification process. An analysis of the effect of the additives indicated that the rational design of electronic and ionic conduction pathways is required for higher cycle performance when using sulfur-rich S-CRs.

Field-assisted sintering technique (FAST) and flash sintering experiments were conducted on hydroxyapatite (HAp) ceramics to attaining highly densified HAp body with uniform microstructure. FAST region, in which the densification was gradually accelerated, was observed from 800 °C under all fields examined. Under the field strength beyond 1000 V·cm⁻¹, the FAST followed by flash sintering took place. The phase decomposition can be effectively suppressed by the FAST/flash sintering. During the FAST region, microstructure remained uniform and the relative density of 94 % was achieved. By the flash sintering at 1000 V·cm⁻¹, the relative density of 97 % was achieved, but inhomogeneous microstructure appeared. By conducting controlled current rate sintering, the densification of the HAp with homogeneous microstructure was attained. The avoidance of current surge and localized current path through the specimen was crucial to attain the uniform, densified microstructure in the HAp ceramics.

In the present study, tracer and conductivity diffusion coefficients (D* and D_σ), and the Haven ratio H_R defined as D*/D_σ have been theoretically estimated in proton-conducting perovskite ceramics using the kinetic Monte Carlo (KMC) simulations. D* was estimated from the mean square displacement of protons in the equilibrium state by the ordinary KMC simulations, while D_σ was estimated from the drift velocity of protons in the non-equilibrium KMC simulations with an applied electric field. Taking proton-conducting yttrium-doped barium zirconate (BaZr_1−xY_xO₃, 0 < x ≤ 0.3) with the cubic perovskite structure as a model system, the D*, D_σ, and H_R of protons were estimated at intermediate temperatures. The estimated H_R are almost unity in the range of 0.99 and 1.04, indicating that the conventional mobility and conductivity estimation using the tracer diffusion coefficient D* through the Nernst-Einstein equation is reasonable approximation for this model system. Exactly, the estimated H_R are slightly higher than unity in the case of high doping levels particularly at low temperatures, which is an opposite trend to the general H_R (≤ 1) in solid state ionic conductors.

Determining the stable atomic structure of grain boundaries (GBs) is one of the most important tasks for computational materials science to comprehensively understand the structure-property relationship of GBs in real polycrystalline materials. In this paper, we revisit a proposed method (PM) that was thought to be ineffective in determining the stable GB structures based on sampling non-identical terminating crystal planes of the two adjoining crystals forming the GB. In contrast to the previous conclusion, we found that the PM is effective regarding both the reproducibility of stable structures and calculation cost. This method could determine the most stable GB structures and energies of not only elemental materials of face-centered-cubic and body-centered-cubic metals, including Cu and Mo, but also a binary ceramic material, MgO. We show that the PM can greatly reduce the number of necessary candidate structures calculated to determine the stable GB structures compared with other brute-force methods sampling the rigid body translation between the two adjoining crystals. We demonstrated that sampling GB structures made of non-identical termination combinations is a useful and effective method to determine the stable GB structures of various materials.

Algorithms of crystal structure prediction produce many different structures, some of which are dynamically unstable. Following the imaginary phonon modes obtained by lattice dynamics calculations, dynamically stable structures can be rationally derived from unstable structures. Following the imaginary phonon modes, however, generally requires lengthy and often prohibitively expensive calculations. In this study, we employ polynomial machine learning potentials to predict globally stable and metastable structures following the imaginary phonon modes. As a result, we discover many dynamically stable and metastable structures efficiently, and the face-centered cubic structure is the globally stable structure consistent with experimental reports for the elemental Cu, Ag, and Au.

Artificial-neural-network (ANN) interatomic potentials for Al–Y–O and Al–Hf–O systems are constructed using density-function-theory (DFT) data and combined with Monte Carlo (MC) simulations in order to predict Y and Hf segregation behavior at the Σ 7(4−510)/[0001] grain boundary (GB) in α-Al₂O₃. The ANN potentials are demonstrated to accurately predict preferential substitutional sites of not only an isolated but also multiple dopant ions. This enables us to circumvent DFT calculations for MC trial moves, thereby greatly reducing computational cost. There is a tendency that both Y and Hf ions substitute for 6-fold Al ions with elongated Al–O bonds at the GB and have coordination numbers greater than 6 after structural relaxation. This may suggest that even at the GB, Y and Hf ions prefer atomic environments in Y- and Hf-containing oxides with 7- and 8-fold coordination. Furthermore, effects of dopant species and concentrations on band-gap reduction at the GB are elucidated by analyzing partial density of states for the dopant-segregated GBs. The ANN-MC method with DFT analysis will pave the way for systematically determining atomic and electronic structures of GBs involving dopants, as demonstrated in this work.

Machine learning potentials (MLPs) are attracting much attention as powerful tools to accurately and efficiently perform atomistic simulations and crystal structure predictions. In this study, we develop a polynomial MLP for the Al–Cu system applicable to the robust global structure search and metastable structure enumeration. We then apply a combination of a global optimization method and the polynomial MLP to the Al–Cu alloy system. As a result of approximately 10¹⁰ times energy computations, the globally-stable and metastable structures are enumerated in the Al–Cu system.

Soft and hard magnetic materials are becoming increasingly important for energy efficiency in transformers, motors, and inductors. To reveal the microscopic origins of their magnetic properties, it is crucial to observe magnetic domain structures with an external magnetic field at high spatial resolution. Differential-phase-contrast scanning transmission electron microscopy (DPC STEM) is expected to be a powerful technique for directly visualizing electromagnetic fields inside materials even down to atomic dimensions. In this study, we investigated the capability of DPC STEM for in-situ observation of soft magnetic materials. We observed three different soft magnetic materials with various coercivities and found clear differences in the observation results. These results suggest that DPC STEM has a great capability to directly reveal the microscopic origin of magnetic properties in magnetic materials.

Oxides containing unusually high-valence transition-metal ions often exhibit charge transitions to relieve the electronic instabilities. A-site-ordered quadruple perovskites LnCu₃Fe₄O₁₂ with the unusually high-valence Fe^3.75+, which are synthesized under high-pressure conditions, show intermetallic-charge-transfer transitions. In this review article, novel thermo-related functional properties induced by the charge transitions in LnCu₃Fe₄O₁₂ are highlighted. A large negative-thermal-expansion behavior was observed at the intermetallic-charge-transfer transition temperature. The negative-thermal-expansion property is primarily caused by the size effect of constituent ions by the charge changes. The property is useful for developing materials to compensate the normal positive thermal expansion. Significant latent heat was also found to be provided by the intermetallic-charge-transfer transition in LnCu₃Fe₄O₁₂. The large latent heat is considered to be related with unusual first-order magnetic entropy change induced by the charge transition. The large entropy change can be utilized for thermal control through a caloric effect, which can make effective energy systems for thermal energy storage and refrigeration.

Tin sulfide (SnS) is a semiconductor composed of abundant and non-toxic elements and has potential applications as a light absorbing layer in thin-film solar cells and a thermoelectric material. While controlling the carrier type (n- or p-type conduction) and carrier concentration of SnS by impurity doping has been intensively studied both experimentally and theoretically since 2010s, no comprehensive discussion of them has been made. This review is motivated to provide researchers with an overview of SnS doping techniques including following topics. The importance and effects of carrier control on the performance of SnS-based photovoltaics and thermoelectric devices are at first discussed. Subsequently, the electrical property of the undoped SnS resulting from its intrinsic defects are summarized. Also, the characteristics of p- and n-type dopings to SnS with various dopants are summarized and compared with the doping systems to other IV–VI group semiconductors, particularly SnSe. The final section presents a perspective on the current status of research in SnS carrier control and potential future research directions.

The copper (Cu) valence greatly influences the transition temperature (T_c) in cuprate superconductors. According to the charge neutralization rule, the Cu valence is calculated from the oxygen content. Previously, we developed the dissolved oxygen (DO) method as a novel oxygen measurement method for La_2−xSr_xCuO₄ and YBa₂Cu₃O_y (YBCO) using a new DO sensor. The measurement time of the DO method is about one-third that of the standard iodometric method, but the difference in the measured Cu valence for YBCO is 0.039. Herein we report that a more accurate method, which combines the dissolved chlorine method and the corrected DO method, improves this difference to 0.013.

Crystalline Cu₂O films were fabricated via the spin-spray method at substrate temperature (T_s) below 90 °C, without the post heat treatment. Grain size, crystal orientation and optical band gap controls of Cu₂O films were achieved by changing T_s. The film orientation was delicately tuned in sequence from {111} to {200} with T_s increasing from 50 to 90 °C. The Cu₂O film fabricated at T_s of 70 °C had a film thickness of 1.19 µm and consisted of a columnar structure with an average diameter size of 0.8 µm. In contrast, the films fabricated at T_s of 90 °C were composed of nanoparticles with diameters less than 0.1 µm. It was observed that a smaller grain size on the film surface corresponded to a wider optical band gap. Notably, the film fabricated at T_s of 50 °C exhibited a relatively wide band gap of 2.97 eV due to the quantum size effect.

Two-types of phase-field (PF) calculations were developed to predict the crystallization of borides. The first calculation used an empirical PF mobility [L_exp = A(k_BTΔT/6π²λ³η)^B], which was determined from experimental crystal growth rates (v_exp). The calculation results for various binary borides such as Li₂O–2B₂O₃, Na₂O–2B₂O₃, Na₂O–4B₂O₃, K₂O–4B₂O₃, BaO–2B₂O₃, and PbO–2B₂O₃, agreed well with the experimental v_exp below their melting points. Furthermore, the A and B values of the L_exp for the borides depended on diffusivity and cation molar mass, including that it is important for cation transfers during crystallization. The second calculation solved the PF equation using versatile PF mobility (L′ ∼ rD/κ²), in which an interfacial process (r) was included. The calculation results agreed well with the first calculation results and the experimental v_exp, except for Li₂O–2B₂O₃. In Li₂O–2B₂O₃, the interfacial process strongly affected the crystal growth rates because of the strong nonlinear phenomenon. For diffusive ceramics such as Li₂O–2B₂O₃, we should use the empirical L_exp. However, the versatile PF equation, which includes the interfacial process (L′) can predict the v_exp of many borides.

Layered sodium titanates are extremely advantageous for use in the energy and environmental fields. Herein, submicron-sized layered sodium titanate crystals were synthesized at low temperatures via solid-state reaction using trisodium citrate as the Na source. Characterization results including in situ observations showed that the decomposition of trisodium citrate proceeded at 300–350 °C, and the resulting activated Na species reacted with TiO₂ at temperatures of 520 °C and above. This study therefore provides an economically viable method for the synthesis of layered titanate materials.

The good correlation between the speed of oxygen-release versus the oxygen-ion conductivity was found in ceria-zirconia under 33 mol % of Ce content. The crystal lattice expansion was also found to affect the speed of oxygen-release in ceria-zirconia with Ce content of 33–66 mol %. Because these properties can be controlled by rare-earth trivalent cation M³⁺-doping in ceria-zirconia, the state of M³⁺ and vacancies formed by substituting with M³⁺ has been investigated in typical model samples of M³⁺-doped ceria-zirconia using X-ray powder diffraction and X-ray absorption fine structure. It was experimentally clear that the lattice constant increased with increasing the ionic radius of M³⁺-doped in (Ce_0.5Zr_0.4M_0.1)O_1.95. It was also found that M³⁺ with higher ligand-field stabilization energy of f-orbitals tended to be fully octahedral-coordinated by eight oxygen ions and form free oxygen vacancies un-associated with M³⁺, possibly leading to the high speed of oxygen-release.

A Fe-modified Na-P1 type artificial zeolite (Fe-P1) was prepared by mixing with the synthesized zeolite powder using chemical reagents and FeCl₃ solution. The anion exchange capacity was generated by the iron hydroxyl group on the zeolite surface. Although the intensity of the X-ray diffraction (XRD) peaks for the zeolite phase decreased with an increase in the concentration of the mixed FeCl₃ solution, the anion exchange ability for the phosphate was improved due to the increase in the surface area. The Fe-P1 zeolite showed a high selectivity for the anions of phosphoric acid and arsenic acid. The anion adsorption capacity was significantly increased under the acidic condition (pH 5) of the solution. Acidic treatment of the Fe-P1 zeolite was also effective for the anion adsorption.

Additive manufacturing by vat-photopolymerization is important technique to prepare designed objects because of its features of availability, low cost, low energy consumption, and high-speed printing. One of the major challenges of this technique is how to expand the chemical composition towards metals and ceramics in addition to organic compounds. In this paper, we report synthesis of highly concentrated nanocolloids of nickel hydroxide acrylate and use them for vat-photopolymerization. Epoxide-mediated basification induced formation of dispersed nickel hydroxide acrylate monolayer/bilayer nanoparticles (diameter of 2.31 nm). The concentration of nanocolloid was prepared as 2.5 mol L⁻¹ (Ni basis), which corresponds to 43 wt % and 30 vol %. The concentrated nanocolloids enabled to produce objects through vat-photopolymerization by using commercially available 3D printers. Addition of small quantity of organic cross-linker efficiently interconnect nanoparticles to form bulky objects. Owing to the organic moiety of nickel hydroxide salt nanoparticles, metal/carbon composites formed by heat-treatment without any reduction gas supply. Further heat-treatment led metal oxide bulky object with macroporous structure.

A novel acetic-acrylic (AA) approach was developed to obtain La_0.6Sr_0.4CoO_3−δ (LSC) using lanthanum oxide, acetate, and acrylic acid as the starting materials. We synthesized several LSC products with varying acrylic acid (L) and metal salt (M) molar ratios (L/M). The precursors and the final products were thoroughly characterized. When the L/M molar ratio is 0.9, the high-purity nano LSC powders were obtained by heating at 900 °C. The conductivity of LSC bulk sample was equal to 2534 and 2430 S cm⁻¹ at 650 and 700 °C, respectively. This sintered LSC was used in a cathode with polarisation resistances (Rp) of 0.190 and 0.084 Ω·cm² at 650 and 700 °C, respectively. It was observed that at 700 and 650 °C, the power density of an anode with a structure that might be defined as Ni-3YSZ/8YSZ/GDC/LSC-0.9 was 947 and 585 mW cm⁻², respectively. Our results revealed that the high-performance LSC powders could be synthesized by the acetic-acrylic synthesis method, applicable to a large scale.

Two types of glass particles were immersed in simulated body fluid (SBF) at 37 °C. Silicate glass 45S5 with a trademark name “Bioglass” only formed hydroxyapatite (HAp) near the particle surface, leaving a large amount of silica gel in the interior. The second glass type was borosilicate glass with a composition of the 45S5 glass in which a major part of SiO₂ was replaced with B₂O₃; in the samples from it, glass was completely replaced with HAp inside the particles. We used Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy (TEM) to characterize the microscopic structure of samples. When the 45S5 glass was immersed in SBF, the PO₄³⁻(Q⁰) in glass quickly formed amorphous calcium phosphate (ACP), a precursor of HAp. Ca²⁺ preferentially coordinated with PO₄³⁻(Q⁰) forming ACP [Ca²⁺–PO₄³⁻(Q⁰)], which is considered stable, where the notation Qⁿ represents the number (n) of the bridging oxygen atoms per PO₄ tetrahedron. The TEM results showed that the columnar crystals of HAp grew along the c-axis. In the borosilicate glass, the reaction is thought to progress to the inside through ion transport into the space where B₂O₃ was eluted.

This paper investigated the effect of two-step ultrasound irradiation (miniaturization and oxidation) on various gallium-based liquefied alloys in ethanol and hydrazine monohydrate at 60 °C. The miniaturization and oxidation behavior of the liquefied alloys were analyzed. In the Ga-based alloy system, the miniaturization process was not as efficient as that of pure gallium due to changes in corrosive properties, surface tension, and viscosity caused by the addition of other metals. In the oxidation step, nanosized crystal grains were abundantly generated at the initial stage, and metal-doped γ-Ga₂O₃ was finally obtained in the Ga–Al and Ga–Mg systems. However, in the Ga–Ag system, the alloy’s oxidation rate was slow, and Ag-doped γ-Ga₂O₃ was not obtained. These results suggest that the redox potential of added metals significantly affects the oxidation behavior. By utilizing this phenomenon, it is possible to synthesize γ-Ga₂O₃ nanoparticles with controlled composition and morphology.