Multinary Compounds Research Articles

Mechanism for Local-Atomic Structure Changes in Chalcogenide-based Threshold-Switching Devices.

Threshold-switching devices based on amorphous chalcogenides are considered for use as selector devices in 3D crossbar memories. However, the fundamental understanding of amorphous chalcogenide is hindered owing to the complexity of the local structures and difficulties in the trap analysis of multinary compounds. Furthermore, after threshold switching, the local structures gradually evolve to more stable energy states owing to the unstable homopolar bonds. Herein, based on trap analysis, DFT simulations, and operando XPS analysis, it is determined that the threshold switching mechanism is deeply related to the charged state of Se-Se homopolar defects. A threshold switching device is demonstrated with an excellent performance through the modification of the local structure via the addition of alloying elements and investigating the time-dependent trap evolution. The results concerning the trap dynamics of local atomic structures in threshold switching phenomena may be used to improve the design of amorphous chalcogenides.

Switching it up: New mechanisms revealed in wurtzite-type ferroelectrics.

Wurtzite-type ferroelectrics have drawn increasing attention due to the promise of better performance and integration than traditional oxide ferroelectrics with semiconductors such as Si, SiC, and III-V compounds. However, wurtzite-type ferroelectrics generally require enormous electric fields, approaching breakdown, to reverse their polarization. The underlying switching mechanism(s), especially for multinary compounds and alloys, remains elusive. Here, we examine the switching behaviors in Al1-xScxN alloys and wurtzite-type multinary candidate compounds we recently computationally identified. We find that switching in these tetrahedrally coordinated materials proceeds via a variety of nonpolar intermediate structures and that switching barriers are dominated by the more-electronegative cations. For Al1-xScxN alloys, we find that the switching pathway changes from a collective mechanism to a lower-barrier mechanism enabled by inversion of individual tetrahedra with increased Sc composition. Our findings provide insights for future engineering and realization of wurtzite-type materials and open a door to understanding domain motion.

Effect of La3+ on the Formation of Endohedral Zintl Clusters Featuring In/Bi Shells.

Investigating the interactions of f-block metal ions with p-block polyanions in multinary cluster compounds is becoming increasingly attractive but remains a challenge in terms of both the synthetic approach and the control of the structures that are formed during the syntheses. So far, two types of reactions were dominant for the formation of corresponding clusters: the reaction of binary anions of p-block elements in 1,2-diamino-ethane (en) solutions or the reaction of organobismuth compounds with corresponding f-block metal complexes in THF. Herein, we report the synthesis of [La@In2Bi11]4- (1) and its doubly μ-Bi-bridged analogue in the doubly [K(crypt-222)]+-coordinated {[K(crypt-222)]2[La@In2Bi11](μ-Bi)2[La@In2Bi11]}4- (2) as their [K(crypt-222)]+ salts [K(crypt-222)]41 and [K(crypt-222)]42, respectively, achieved by reactions of [InMes3] and [La(C5Me4H)3] (Mes = mesityl, C5Me4H = tetramethylcyclopentadienyl) with K10Ga3Bi6.65/crypt-222 (crypt-222 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) in en. In the absence of [La(C5Me4H)3], the otherwise unchanged reactions afford the anions [Bi6(InMes)(InMes2)]3- (3) and [Mes3In-InMes3]2- (4) instead, which can be isolated as their [K(crypt-222)]+ salts [K(crypt-222)]33 and [K(crypt-222)]24·tol (tol = toluene), respectively. The {Bi6} fragment observed in anion 3 is assumed to be one of the key intermediates not only toward the formation of 1 and 2 but also on the way to more general bismuth rich compounds.

Spectrally narrow band-edge photoluminescence from AgInS2-based core/shell quantum dots for electroluminescence applications.

This study presents a facile synthesis of cadmium-free ternary and quaternary quantum dots (QDs) and their application to light-emitting diode (LED) devices. AgInS2 ternary QDs, developed as a substitute for cadmium chalcogenide QDs, exhibited spectrally broad photoluminescence due to intrinsic defect levels. Our group has successfully achieved narrow band-edge PL by a coating with gallium sulfide shell. Subsequently, an intrinsic difficulty in the synthesis of multinary compound QDs, which often results in unnecessary byproducts, was surmounted by a new approach involving the nucleation of silver sulfide followed by material conversion to the intended composition (silver indium gallium sulfide). By fine-tuning this reaction and bringing the starting material closer to stoichiometric compositional ratios, atom economy was further improved. These QDs have been tested in LED applications, but the standard device encountered a significant defective emission that would have been eliminated by the gallium sulfide shells. This problem is addressed by introducing gallium oxide as a new electron transport layer.

Fabrication of Quantum Dot LED Display with Multinary Compound Semiconductor Quantum Dots

Fabrication of Quantum Dot LED Display with Multinary Compound Semiconductor Quantum Dots

Colloidal Synthesis and Photoluminescence Property of Near-IR-Responsive Ag8GeS6 Quantum Dots

Semiconductor nanocrystals of a few nanometers in size, called quantum dots (QDs), exhibit unique photochemical properties due to quantum size effect. In recent years, high-quality near-infrared responsive QDs such as CdTe and PbS have been used for wide-ranged applications from light-energy conversions to biomedical applications. However, the contents of highly toxic elements, Cd and Pb, restrict their practical use. On the other hand, group IV-based multinary compound semiconductors, such as Ag2ZnSnS4, Ag8SnS6, and Ag8GeS6, have attracted much attention because of their less toxicity and light absorption property in visible and near-IR region. However, there are only a few reports to prepare size-quantized nanocrystals for tuning their photoelectrochemical properties. In this study, we report the preparation of Ag8GeS6 core and Ag8GeS6@ZnS core/shell QDs using a feasible liquid-phase chemical synthesis method.As a moisture and air stable Ge precursor, Ge(gly)2(H2O)2 was prepared by the literature method with slight modification[1]. Precursor powders of Ge(gly)2(H2O)2, silver(I) diethyldithiocarbamate, and thiourea were dispersed in a mixture solvent of 1-dodecanethiol and oleylamine, followed by the heat treatment at 423 K for 20 min. Thus-obtained QDs were isolated from the reaction solution by the addition of methanol and ethanol as a non-solvent. Then, the obtained QDs were finally dispersed in chloroform. The obtained Ag8GeS6 QDs were further surface-coated with thin ZnS layer to form Ag8GeS6@ZnS core/shell QDs.The onset wavelengths in the absorption spectra of Ag8GeS6 and Ag8GeS6@ZnS were observed at 850 nm and 830 nm, respectively. The XRD analysis showed that the obtained nanocrystals had an orthorhombic Ag8GeS6 crystal structure. TEM measurements revealed that the prepared Ag8GeS6 QDs had an average particle size of 4.53 nm while that of Ag8GeS6@ZnS was 5.80 nm. From the difference between the sizes before and after ZnS coating, we estimated the ZnS shell thickness of Ag8GeS6@ZnS to 0.63 nm. The energy gap of Ag8GeS6 QDs was slightly decreased from 1.45 eV to 1.37 eV with an increase in Ge/(Ge+Ag) ratio. Ag8GeS6 QDs with Ge/(Ge+Ag) = 0.8 exhibited a broad photoluminescence (PL) peak at 850 nm with PLQY of about 25%. The surface coating with ZnS remarkably increased the PLQY to 65%, which was considerably high in comparison to those of near-IR-emissive multinary QDs in our previous papers such as Ag–In–Ga–Se and Ag–In–Ga–S–Se QDs [2,3]. Thus, the present Ag8GeS6@ZnS QDs seem to be a promising probe for bio-imaging with near-IR photoluminescence.[1] A.S.R. Chesman, et al., Chem. Mater, 26, 5726 (2014).[2] T. Kameyama, et al., ACS Appl. Nano Mater, 3, 3275-3287 (2020).[3] N. Rismaningsih, et al., J. Mater. Chem. C, 9, 12791-12801 (2021).

Cell voltage of mixed conductors under partially frozen conditions

Partially frozen-in states are rather the rule than the exception. Coexistence between equilibrium states and frozen-in states is relevant in view of the diversity and complexity of charge carriers, or sublattices, especially in multinary compounds, but also with respect to differently equilibrated spatial regions. This contribution deals with the open circuit potential of samples where only surface-near regions feel the outer partial pressure, or more generally, the component chemical potentials, established by the electrodes. In view of the significance of such measurements for separating ionic and electronic conductivity contributions, and the kinetic difficulties in getting full equilibration near room-temperature, the value of these considerations is obvious. The necessary relations are derived, or their derivations are sketched within the framework of linear force–flux laws. An account is made of recent emf measurements of hybrid halide perovskites, and a refinement of their standard defect diagram is recommended.

Effects of Mn-substitution on magnetic properties of R6TX2-based (R = Gd–Dy, T = Mn–Ni; X = Sb and Te) multinary compounds

The multinary compounds Dy6Mn0.3Fe0.7Sb2, Dy6MnSbTe, {Gd, Tb}6FeSbTe, Gd3Tb3FeSbTe, {Gd, Tb}2Dy4Mn0.25Fe0.75Sb2, Gd2Tb4Mn0.25Fe0.75SbTe, Tb6Mn0.25{Fe, Co, Ni}0.75SbTe, Tb6Mn0.4Co0.6SbTe and Tb6Mn0.5Ni0.5SbTe crystallize in the Zr6CoAl2-type structure (ordered variant of the Fe2P structure) (space group P-62m, N 189, hP9). The polycrystalline samples Gd3Tb3FeSbTe, {Gd, Tb}2Dy4Mn0.25Fe0.75Sb2, Gd2Tb4Mn0.25Fe0.75SbTe, Tb6Mn0.25{Fe, Co, Ni}0.75SbTe, Tb6Mn0.4Co0.6SbTe and Tb6Mn0.5Ni0.5SbTe exhibit high-temperature ferromagnetic ordering and low-temperature field sensitive transformation of magnetic ordering. Of these compounds, Gd2Tb4Mn0.25Fe0.75SbTe shows the highest Curie temperature at 292 K with the low-temperature transformation of magnetic ordering at 60 K. Gd3Tb3FeSbTe displays the strongest hard magnetic properties at low temperatures with residual magnetization per formula unit of 16 μB and coercive field of 16 kOe at 2 K. Tb6Mn0.25Ni0.75SbTe and Tb6Mn0.4Co0.6SbTe exhibit large magnetocaloric effect with magnetic entropy change of −4.6 J/kg⋅K and −4.5 J/kg⋅K, respectively, around Curie temperature in a field change of 50 kOe.The specific features of Mn-catalysis/substitution for magnetic properties of these compounds are viewed and discussed.

Tuning Interfacial Chemistry to Direct the Electrosynthesis of Metal Oxide Semiconductors.

ConspectusMetal oxide semiconductors have many features that make them attractive for both fundamental and applied studies. For example, these compounds contain elements (e.g., Fe, Cu, Ti, etc.) that are derived from minerals rendering them earth-abundant and, most often, are also not toxic. Therefore, they have been examined for possible applicability in a very diverse range of technological applications including photovoltaic solar cells, charge storage devices, displays, smart windows, touch screens, etc. The fact that metal oxide semiconductors have both n- and p-type conductivity makes them amenable for use as hetero- or homojunctions in microelectronic devices and as photoelectrodes in solar water-splitting devices. This Account presents a review of collaborative research on the electrosynthesis of metal oxides from our respective groups against the backdrop of key developments on this topic. The many variants that interfacial chemical modification schemes offer are shown herein to lead to the targeted synthesis of a wide array of not only simple binary metal oxides but also more complex chemistries involving multinary compound semiconductors and alloys.This Account presents our perspective on how parallel developments in the understanding of and ability to manipulate electrode-electrolyte interfaces have correspondingly enabled the innovation of a broad array of electrosynthetic strategies. These coupled with the advent of versatile tools to probe interfacial processes (undoubtedly, a child of the nanotechnology "revolution") afford an operando examination of how effective the strategies are to secure the targeted metal oxide product as well as the mechanistic nuances. Flow electrosynthesis, for example, removes many of the complications accruing from the accumulation of interfering side products─veritably, this is an Achilles heel of the electrosynthesis approach. Coupling flow electrosynthesis with downstream analysis tools based on spectroscopic or electroanalytical probes opens up the possibility of immediate process feedback and optimization. The combination of electrosynthesis, stripping voltammetry, and electrochemical quartz crystal nanogravimetry (EQCN), either in a static or in a dynamic (flow) platform, is shown below to offer intriguing possibilities for metal oxide electrosynthesis. While many of the examples below are based on our current and recent research and in other laboratories, unlocking even more potential will hinge on future refinements and innovations that surely are around the corner.

Thermoelectric Silver-Based Chalcogenides.

Heat is abundantly available from various sources including solar irradiation, geothermal energy, industrial processes, automobile exhausts, and from the human body and other living beings. However, these heat sources are often overlooked despite their abundance, and their potential applications remain underdeveloped. In recent years, important progress has been made in the development of high-performance thermoelectric materials, which have been extensively studied at medium and high temperatures, but less so at near room temperature. Silver-based chalcogenides have gained much attention as near room temperature thermoelectric materials, and they are anticipated to catalyze tremendous growth in energy harvesting for advancing internet of things appliances, self-powered wearable medical systems, and self-powered wearable intelligent devices. This review encompasses the recent advancements of thermoelectric silver-based chalcogenides including binary and multinary compounds, as well as their hybrids and composites. Emphasis is placed on strategic approaches which improve the value of the figure of merit for better thermoelectric performance at near room temperature via engineering material size, shape, composition, bandgap, etc. This review also describes the potential of thermoelectric materials for applications including self-powering wearable devices created by different approaches. Lastly, the underlying challenges and perspectives on the future development of thermoelectric materials are discussed.

Suppressing Charged Cation Antisites via Se Vapor Annealing Enables p-Type Dopability in AgBiSe2 -SnSe Thermoelectrics.

Cation disordering is commonly found in multinary cubic compounds, but its effect on electronic properties has been neglected because of difficulties in determining the ordered structure and defect energetics. An absence of rational understanding of the point defects present has led to poor reproducibility and uncontrolled conduction type. AgBiSe2 is a representative compound that suffers from poor reproducibility of thermoelectric properties, while the origins of its intrinsic n-type conductivity remain speculative. Here, it is demonstrated that cation disordering is facilitated by BiAg charged antisite defects in cubic AgBiSe2 which also act as a principal donor defect that greatly controls the electronic properties. Using density functional theory calculations and in situ Raman spectroscopy, how saturation annealing with selenium vapor can stabilize p-type conductivity in cubic AgBiSe2 alloyed with SnSe at high temperatures is elucidated. With stable and controlled hole concentration, a peak is observed in the weighted mobility and the density-of-states effective mass in AgBiSnSe3 , implying an increased valley degeneracy in this system. These findings corroborate the importance of considering the defect energetics for exploring the dopability of ternary thermoelectric chalcogenides and engineering electronic bands by controlling self-doping.

Discovery of Two-Dimensional Multinary Component Photocatalysts Accelerated by Machine Learning.

Searching for novel and high-performance two-dimensional (2D) materials is an important task for photocatalytic applications. Although multinary compounds exhibit more diversity in structure and properties in comparison to binary 2D materials, they are comparatively under-studied. Herein, using a machine-learning (ML) technique and high-throughput screening, we develop an efficient approach to accurately predict 2D multicomponent photocatalysts. Over 4000 monolayers are examined, and 75 multinary compounds are identified for photocatalytic applications. Considering our predictions, we find that the ternary and quaternary compounds A2P2X6 and ABP2X6 with A = Cu/Zn/Ge/Ag/Cd, B = Ga/In/Bi, and X = S/Se exhibit superior properties, making them promising candidates for overall water splitting. Thus, our work provides an efficient way to explore novel photocatalysts, which could stimulate further theoretical and experimental investigations on 2D multinary compounds for application in photocatalytic water splitting.

Structural diversity among multinary pnictide oxides: a minireview focused on semiconducting and superconducting heteroanionic materials

Abstract Incorporating different anions with varied ionic sizes and charges is a rapidly growing approach to bring out unusual physical properties among various classes of solid-state materials, pnictides and chalcogenides in particular. This minireview is focused on hetero-anionic materials based on the pnictogens, which have been demonstrated to offer an impressive diversity of crystal chemistry and electronic structures. In addition, many pnictide oxides or oxypnictides, over the course of the last decade, have been shown to exhibit a broad spectrum of superconducting, magnetic, and semiconducting properties. However, the structural diversity of the mixed-anion materials is far greater than the several known structure types, or their variants, of the well-known layered superconductive materials. Therefore, with this treatise, we aim to provide a comprehensive overview of the crystal chemistry of pnictide oxides by recounting almost 40 different structures of such ternary and multinary compounds. In addition to the structural aspects, we also highlight some of the challenges associated with the synthesis, and briefly summarize reported, to date, physical properties of this remarkable class of solids.

Effect of Self‐Seed Inducing on the Growth Mechanism and Photovoltaic Performance of Cu2ZnSnSe4 Thin Films

The self‐seed inducing grain growth mechanism for a Cu2ZnSnSe4 (CZTSe) thin film is explored via the existence of the fine‐grain CZTSe synthesized spontaneously at a relatively low soft‐selenization temperature of 300°C. Fine control over the elementary proportion and distribution of metal precursors is an important approach for obtaining the self‐seed inducing effect after soft selenization. Herein, a multiple‐cycle metal stack precursor, prepared by a weighting method, is developed to control the elementary proportion and distribution. By shortening the diffusion distance to produce a self‐seed inducing effect at soft selenization, the formation of detrimental intrinsic defects and secondary phases is effectively suppressed, contributing to the optimization of the CZTSe absorber back contact and surface. Consequently, the conductivity of the grain interiors and boundaries of the absorber layer is enhanced, the electric potential and roughness of the surface are reduced considerably, and the minority carrier lifetime of the layer is increased. When the number of stacked cycles increases from 1 to 7, the champion efficiency of CZTSe solar cell improves from 2.97% to 8.05% with a significant decrease in the open circuit voltage deficit from 0.831 to 0.617 V. These results may prove useful for developing a wider range of multinary compound semiconductor devices.

Materials science of chalcopyrite-type and multinary solar cells compounds: crystal structure and electronic structure of CISe, CZTS, CTS, and the related compounds

Materials science of chalcopyrite-type and multinary solar cells compounds: crystal structure and electronic structure of CISe, CZTS, CTS, and the related compounds

Optical deciphering of multinary chiral compound mixtures through organic reaction based chemometric chirality sensing

The advances of high-throughput experimentation technology and chemometrics have revolutionized the pace of scientific progress and enabled previously inconceivable discoveries, in particular when used in tandem. Here we show that the combination of chirality sensing based on small-molecule optical probes that bind to amines and amino alcohols via dynamic covalent or click chemistries and powerful chemometric tools that achieve orthogonal data fusion and spectral deconvolution yields a streamlined multi-modal sensing protocol that allows analysis of the absolute configuration, enantiomeric composition and concentration of structurally analogous—and therefore particularly challenging—chiral target compounds without laborious and time-consuming physical separation. The practicality, high accuracy, and speed of this approach are demonstrated with complicated quaternary and octonary mixtures of varying chemical and chiral compositions. The advantages over chiral chromatography and other classical methods include operational simplicity, increased speed, reduced waste production, low cost, and compatibility with multiwell plate technology if high-throughput analysis of hundreds of samples is desired.

Phase Pure Silver Pyrovanadate (Ag4V2O7) Thin Films: Synthesis via a Hybrid Cathodic/Anodic Approach and Characterization

Combining two or more binary compounds to generate a multinary compound is a strategy for enhancing the photoelectrochemical (PEC) performance and properties of the parent binary compounds. In this vein, multinary compound semiconductors have recently come under the spotlight in a variety of device applications. In particular, the low energy band gap of the Ag-V-O ternary family (Ag3VO4, Ag4V2O7, AgVO3, Ag2V4O11, and AgV7O18) has recently sparked interest in using these visible light active semiconductor for photovoltaic solar cells, solar water splitting, CO2 photoreduction, and environmental remediation applications. In particular, Ag4V2O7, a visible light active semiconductor with a low band gap (2.49 eV) has been synthesized in powder form using solid state, hydrothermal, and precipitation methods.1,2 However, for device applications, deposition techniques that facilitate direct synthesis of semiconductor in film form, are attractive.In this vein, electrochemical deposition is a fast, low temperature, and scalable method to prepare large active area films of a given semiconductor. Therefore, this paper presents a hybrid cathodic and anodic route for the electrodeposition of Ag4V2O7 thin films and its subsequent physical and optoelectronic characterizations. Ag4V2O7 thin film on fluorine-doped tin oxide (FTO) substrate was synthesized using a hybrid cathodic and anodic route previously developed in our laboratory.3 In the cathodic step, a metallic silver thin film was electrosynthesized from silver ions in a nonaqueous medium on fluorine-doped tin oxide (FTO) support. In the anodic step, the generated silver ion (Ag+) from anodic stripping of the silver thin film in a pyrovanadate ion (V2O7 4-)containing-solution resulted in an in situ precipitation reaction with V2O7 4- to form Ag4V2O7 thin film on FTO. Electrochemical quartz crystal nanogravimetry (EQCN) confirmed one and four electron stoichiometry for the cathodic and anodic steps respectively.Energy-dispersive X-ray analysis (EDX) of as-prepared sample gave the Ag/V ratio: 1.95 ± 0.02, close to the expected stoichiometric Ag/V ratio for Ag4V2O7. X-ray diffraction analyses of the as-synthesized sample significantly confirmed that room temperature electrodeposited sample was crystalline and phase-pure. To measure the direct and indirect energy band gaps, Tauc plots were constructed from diffuse reflectance spectroscopy (DRS) data. The estimated direct and indirect optical transition energies of Ag4V2O7 thin films were 2.58 ± 0.04 and 2.52 ± 0.02 eV respectively. A valence band energy position as -4.88 ± 0.03 eV (on the vacuum energy scale) was estimated for Ag4V2O7 using atmospheric photoemission spectroscopy (APS) results. By combining the DRS and APS results, the calculated conduction band edge position of Ag4V2O7 was determined to be -2.36 eV on the vacuum energy scale. Kelvin-probe measurement located the Fermi level of silver pyrovanadate thin films at -4.82 ± 0.02 eV on the vacuum energy scale. The corresponding EF for Ag4V2O7 was only 0.06 eV above the valence band position consistent with a moderately-doped p-type semiconductor. These new results will be discussed in the framework of the application of silver pyrovanadate for PEC reduction processes such as hydrogen evolution or CO2 reduction.

Overcoming Phase‐Purity Challenges in Complex Metal Oxide Photoelectrodes: A Case Study of CuBi2O4

AbstractThe widespread application of solar‐water‐splitting for energy conversion depends on the progress of photoelectrodes that uphold stringent criteria from photoabsorber materials. After investigating almost all possible elemental and binary semiconductors, the search must be expanded to complex materials. Yet, high structural control of these materials will become more challenging with an increasing number of elements. Complex metal‐oxides offer unique advantages as photoabsorbers. However, practical fabrication conditions when using glass‐based transparent conductive‐substrates with low thermal‐stability impedes the use of common synthesis routes of high‐quality metal‐oxide thin‐film photoelectrodes. Nevertheless, rapid thermal processing (RTP) enables heating at higher temperatures than the thermal stabilities of the substrates, circumventing this bottleneck. Reported here is an approach to overcome phase‐purity challenges in complex metal‐oxides, showing the importance of attaining a single‐phase multinary compound by exploring large growth parameter spaces, achieved by employing a combinatorial approach to study CuBi2O4, a prime candidate photoabsorber. Pure CuBi2O4 photoelectrodes are synthesized after studying the relationship between the crystal‐structures, synthesis conditions, RTP, and properties over a range of thicknesses. Single‐phase photoelectrodes exhibit higher fill‐factors, photoconversion efficiencies, longer carrier lifetimes, and increased stability than nonpure photoelectrodes. These findings show the impact of combinatorial approaches alongside radiative heating techniques toward discovering highly efficient multinary photoabsorbers.

Mechanistic origin of the time-dependence of the open-circuit voltage of a galvanic cell involving a ternary or higher compound.

It has previously been predicted [H.-I. Yoo and M. Martin, Phys. Chem. Chem. Phys., 2010, 12, 14699] and observed [E. Kim, et al., Solid State Ionics, 2013, 235, 22] that the open-circuit voltage U of a galvanic cell, involving a ternary or higher compound with more than one kind of mobile ionic carrier, is path- and time-dependent upon imposition or removal of the mobile components' chemical potential differences, in contradistinction to the cell involving a binary compound. This has been attributed [H.-I. Yoo and M. Martin, Phys. Chem. Chem. Phys., 2010, 12 14699; J.-Y. Yoon, et al., Solid State Ionics, 2012, 213, 22] to the decoupled redistributions of multiple mobile components or multi-fold relaxation. We hereby experimentally demonstrate with SrTi0.982Al0.018O3-Δ, known to have an appreciable water solubility depending on temperature, that introduction of a secondary ionic carrier H+ in addition to the native O2- indeed renders the otherwise time-independent U time-dependent; and that this phenomenon may, thus, be employed to probe the presence of a secondary ionic carrier, e.g., H+ in addition to the primary O2- in BaTi0.982Al0.018O3-Δ whose water solubility is yet to be known. The temporal behavior of U of SrTi0.982Al0.018O3-Δ subjected to the two fixed chemical potential differences, ΔμO and ΔμH, is precisely delineated in terms of two-fold relaxation of H and O, yielding their chemical diffusivity values, and consequently, the ambiguity with the EMF-method to determine the ionic transference numbers of a multinary compound is cleared away.

Training machine-learning potentials for crystal structure prediction using disordered structures

Prediction of the stable crystal structure for multinary (ternary or higher) compounds with unexplored compositions demands fast and accurate evaluation of free energies in exploring the vast configurational space. The machine-learning potential such as the neural network potential (NNP) is poised to meet this requirement but a dearth of information on the crystal structure poses a challenge in choosing training sets. Herein we propose constructing the training set from densityfunctional-theory (DFT) based dynamical trajectories of liquid and quenched amorphous phases, which does not require any preceding information on material structures except for the chemical composition. To demonstrate suitability of the trained NNP in the crystal structure prediction, we compare NNP and DFT energies for Ba2AgSi3, Mg2SiO4, LiAlCl4, and InTe2O5F over experimental phases as well as low-energy crystal structures that are generated theoretically. For every material, we find strong correlations between DFT and NNP energies, ensuring that the NNPs can properly rank energies among low-energy crystalline structures. We also find that the evolutionary search using the NNPs can identify low-energy metastable phases more efficiently than the DFTbased approach. By proposing a way to developing reliable machine-learning potentials for the crystal structure prediction, this work will pave the way to identifying unexplored multinary phases efficiently.