Sequence Of Structural Phase Transitions Research Articles

Synthesis and Characterization of the Electrical and Energy Storage Properties of New Barium Titanate - Europium Titanate Solid Solution

In the present work, the investigation of the structural, dielectric, ferroelectric and energy storage properties of polycrystalline samples of (1-x)BaTiO3 – xEuTiO3 (BT-ET) solid solution materials prepared by conventional solid-state reaction method has been carried out. X-ray diffraction analyses have revealed the formation of a single-phase tetragonal structure with the P4mm space group. Furthermore, the temperature dependence of the dielectric constants marked the presence of the following sequence of structural phase transitions, namely from rhombohedral to orthorhombic, from orthorhombic to tetragonal and from tetragonal to cubic phase transitions with the increase of temperature. A diffuse phase transition has been observed from the dielectric permittivity peak and has been analyzed using the modified Curie-Weiss law and the degree of diffuseness is found to be in the range of 1.16 - 1.76 due to the existence of different states of polarization. A phase diagram has been established based on the temperature-dependent dielectric permittivity studies. The room temperature ferroelectric properties point to a coercive field larger than that of BaTiO3 ceramics. Broad dielectric peaks associated with diffuse phase transition appear in a wide temperature range (40 - 100 °C) with the highest dielectric permittivity ε’ = 6498 found in the x = 0.05 ceramics. Moreover, an improved energy storage performance is obtained in the 0.95BaTiO3-0.05EuTiO3 ceramic with a recoverable energy density of Wrec = 0.797 J/cm3, coupled with an efficiency η = 73% at 170 kV/cm and the highest storage energy density of Wst = 1.571 J/cm3 is obtained for 0.90BaTiO3-0.10EuTiO3, which is superior to other lead-free BT-based ceramics. All these features demonstrate that the BT-ET ceramics can be widely used in energy storage applications and also in high-temperature multilayer capacitors for automotive, aerospace and related industries.

Sequence of Structural and Magnetic Phase Transitions in (NO)Mn6(NO3)13.

New nitrosonium manganese(II) nitrate, (NO)Mn6(NO3)13, has been synthesized and structurally characterized. In the temperature range of 45-298 K, the crystal is hexagonal (centrosymmetric sp. gr. P63/m). Mn2+ ions are assembled into tubes along axis c with both NO3- filling and coating. The nitrosonium cation is located in the framework cavity and is disordered by a 3-fold axis. At the temperature TS1 = 190 K, a structural phase transition related to the libration of the intertube NO3 group and a small variation of Mn polyhedron is observed. Moreover, the anomalies in physical properties of (NO)Mn6(NO3)13 allow suggesting that ordering of NO+ units occurs at low temperatures. The antiferromagnetic ordering in this compound is preceded by the formation of a short-range correlation regime at about 25 K and takes place in two steps at TN1 = 12.0 K and TN2 = 8.4 K.

Thickness dependence of optical and electronic properties of FeCl2 films under high pressure

In this study, we propose an unconventional approach to investigate the pressure-induced changes in crystal structure, electrical transport, and optical bandgap by examining bulk FeCl2 and FeCl2 films with a thickness of 600 nm. Our analysis involved Raman spectroscopy, electrical transport measurements, and Ultraviolet–visible (UV–vis) absorption spectroscopy. Analyzing the Raman spectroscopy data, we discovered subtle distinctions in the sequence of structural phase transitions between bulk FeCl2 and the 600 nm thick film of FeCl2 under varying pressures. Specifically, while bulk FeCl2 underwent an insulating-to-metal transition at 52 GPa, the film of FeCl2 maintained its semiconductor behavior even at pressures as high as 60 GPa. Furthermore, by studying the optical absorption spectra, we observed a consistent decrease in the direct band gap of bulk FeCl2 with increasing pressure. In contrast, the film of FeCl2 exhibited an increase in the optical band gap beyond 34.1 GPa. These remarkable findings offer valuable insights into the manipulation of the mechanical, electrical, and optical properties of layered nanomaterials.

Thorium dicarbide under high pressure and high temperature: Ab initio investigation

A systematic study on the structural stability of thorium dicarbide (ThC2) under hydrostatic compression has been carried out by exploiting the evolutionary structure search algorithm as implemented in the universal structure predictor: evolutionary Xtallography (USPEX) code in conjunction with the ab initio electronic band structure calculation method. At ambient conditions, ThC2 exists in a monoclinic crystallographic phase with space group (SG) C2/c. Our calculations under generalized gradient approximation (GGA) predict the high-pressure structural sequence of monoclinic-I (SG C2/c) → monoclinic-II (SG C2/m) → orthorhombic-I (SG Pmma) → orthorhombic-II (SG Immm) → hexagonal (SG P6/mmm) for this material with transition pressures of ∼3.3, 58.3, 191.6, and 255 GPa, respectively. Out of this theoretically predicted high-pressure structural phase transition sequence, only the first transition, i.e., monoclinic-I → monoclinic-II, could be compared with the available high-pressure experimental study by Guo et al. [Sci. Rep. 7, 45872 (2017)]. The theoretically determined phase transition qualitatively agrees with the experimental results [Y. Guo et al. Sci. Rep. 7, 45872 (2017)]. Interestingly, our predicted intermediate orthorhombic-I (SG Pmma) phase has an enthalpy lower than that of the previously predicted orthorhombic Cmmm phase by Guo et al. [Sci. Rep. 7, 45872 (2017)]. The high-pressure structural sequence so predicted through static lattice calculations has been further substantiated by confirming the elastic and lattice dynamic stability of each structure in the pressure regime of its structural stability. Additionally, the superconducting transition temperature for all these structures has been determined and it is found that the monoclinic-II (C2/m) phase has the highest transition temperature of 17 K at 5 GPa. Furthermore, the thermo-physical properties along with the temperature-induced phase transitions in ThC2 have also been investigated through both the lattice dynamic simulations (within quasi-harmonic approximation) and ab initio molecular dynamics simulations.

Effect of deuteration on the barocaloric properties of complex vanadates (NH4)3VOxF6−x (x: 1, 2)

We report on the analysis of intensive and extensive barocaloric properties and their sensitivity to deuteration of complex oxyfluorides (NH4)3VOxF6−x (x: 1, 2) undergoing a similar sequence of structural phase transitions. Due to the high sensitivity to hydrostatic pressure and the strong disordering of six-coordinated anionic fluoro-oxygen species, (NH4)3VO2F4 and (ND4)3VO2F4 crystals demonstrate the highest barocaloric efficiency at low pressure, p = 0.1 GPa, during the phase transition from the initial cubic phase: barocaloric coefficients reach large values |ΔSBCE|/p ≈ 400 J/(kg K GPa) and ΔTAD/p ≈ 80 K/GPa. Anionic, [VOF5] → [VO2F4], and cationic, [ND4] → [NH4] substitutions are accompanied by a decrease in the disorder of structural units in the cubic phase, which leads to a decrease in changes in entropy and temperature under pressure. The contribution of thermal expansion of the crystal lattice to the total intensive and extensive barocaloric effects is large and amounts to about 30–40%.

Pressure-directed mixed ionic–electronic to pure electronic conduction transition and enhanced grain boundary conductivity in solid electrolyte CdMoO4

Scheelite ABO4-type solid electrolytes have attracted much attention for potential applications as oxygen ionic conductors of solid oxide fuel cells. Herein, a systematic study was carried out on the electrical transport properties of CdMoO4 under high pressure by impedance spectroscopy measurements and theoretical calculations. The sequence of structural phase transitions at pressures was determined as I41/a → C2/c → P21/c by the Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO) method. A pressure-induced conduction transition from mixed ionic–electronic to pure electronic conduction was observed. Below 25.6 GPa, O2− ions play a major role in the electrical transport process. The microscopic transport mechanism was analyzed with grain boundary energies and migration energy barriers. Above 26.9 GPa, the grain boundary response was weakened significantly after a pressure cycle, and the grain boundary conductivity increased by about three times due to pressure. These results provide guidelines for the optimization and application of scheelite ABO4-based oxygen ionic conductors in solid oxide fuel cells.

Structural phase transition and superconductivity of ytterbium under high pressure

Recent advances in theory and experiment declare the rare-earth (RE) hydrogen-rich compound $\mathrm{La}{\mathrm{H}}_{10}$ is a near room-temperature superconductor under high pressure. To understand the underlying mechanism of superconductivity and explore the crucial role of lanthanides in forming the RE-based polyhydrides, we here perform a theoretical study on the structural phase transition and superconductivity of late lanthanide ytterbium (Yb) metal under high pressure up to 240 GPa. Two alternative structures, $R\overline{3}m$ and $I4/mmm$ phases, of Yb are presented. Most interestingly, the $P{6}_{3}/mmc$ phase of Yb is serendipitously discovered to be a superior superconductor with a critical temperature value of 19.5 K at 160 GPa, which is higher than other known RE elemental superconductors. The present findings establish an alternative structural phase transition sequence of Yb, which offers insights for further understanding the vital physics mechanisms of a lanthanide-based superconductor.

Symmetry and strain analysis of combined electronic and structural instabilities in tungsten trioxide, WO3

Lattice parameter data from the literature have been used to provide a complete description of spontaneous strain variations across each of the six known phase transitions of WO3 in the temperature interval 5–1273 K. Analysis of strain/order parameter coupling reveals the character of each phase transition, a unified description of strain across the full temperature range, the relationship between strain and electronic effects, and new insights into the strain gradients likely to be present in each of the different domain walls that develop in four different ferroelastic phases. Tetragonal and orthorhombic shear strains have values of 4%–6% and 2%–3%, respectively, and are dominated by coupling with the order parameter for antiferroelectric-type displacements. Conversely, shear strains, e4, e5, and e6, of up to 2% are controlled by octahedral tilting. Changes in electronic structure and properties have been related back to the susceptibility of W6+ to develop cooperative second-order-Jahn–Teller distortions. Proximity to tilt instabilities along with group–subgroup relationships in the P4/nmm parent structure results in two overlapping sequences of structural phase transitions, which differ in the form of their electronic structure. The possibility of a ground state structure in space group P21/c can be rationalized in terms of the efficiency by which different combinations of shearing and tilting of the WO6 octahedra can reduce the unit cell volume and would imply that WO3 has a re-entrant phase transition. Gradients in up to three order parameters coupled with gradients in strain of up to 12% across ferroelastic domain walls indicate that the different ferroelastic phases of WO3 should have domain walls with varied and potentially exotic electronic properties for device applications such as in nanoelectronics and neuromorphic computing.

Revisiting structural phases in some perovskites: The case of BaCeO3

An effective Hamiltonian is developed and used to investigate the different equilibrium phases that $\mathrm{Ba}\mathrm{Ce}{\mathrm{O}}_{3}$ can possess, as a function of temperature. Such atomistic technique predicts that monodomain $\mathrm{Ba}\mathrm{Ce}{\mathrm{O}}_{3}$ adopts a phase transition sequence that differs from the one commonly experimentally reported in this specific important perovskite, even if the end members of this sequence (namely, the high-temperature cubic $Pm\overline{3}m$ state and the orthorhombic $Pbnm$ ground state) are identical between our simulations and measurements. In contrast with this experimental phase transition sequence, the predicted one is, in fact, in line with a rule denoted here as ``the gradual tilting rule'' that guides the progressive change of oxygen octahedral tiltings about the three Cartesian axes from $Pm\overline{3}m$ to $Pbnm$. The fact that this rule is obeyed in many perovskites, along with some of our analyses and previous works, leads us to strongly suggest that intermediate phases experimentally reported in $\mathrm{Ba}\mathrm{Ce}{\mathrm{O}}_{3}$ pertain to multidomains, twinning, and/or antiphase boundaries. Such suggestion should also apply to other perovskites for which the structural phase transition sequence does not follow ``the gradual tilting rule.''

Local insight to the structural phase transition sequence of Bi2Se3 under quasi-hydrostatic and nonhydrostatic pressure

High-pressure behaviors of Bi2Se3, as one of layered 3D topological insulators, has attracted tremendous interest recent years. However, the phase transition sequence of Bi2Se3 remain controversial. In this work, we explore the structural phase sequence of topological insulator Bi2Se3 using high-pressure x-ray absorption fine structure (XAFS) spectroscopy under quasi-hydrostatic and nonhydrostatic pressure up to 42 GPa. By examining the XAFS features, we find that the appearance of C2/c phase of Bi2Se3 is strongly dependent on pressure condition, C2/c phase of Bi2Se3 only exists under quasi-hydrostatic pressure condition. The phonon dispersion calculations also show that C2/c phase is dynamic unstable. Furthermore, we confirm that Bi2Se3 possesses I4/mmm phase rather than Im-3m and 9/10-fold C2/m phase at high pressure. Combining the experimental and theoretical results, we determine the structural phase transition sequence for Bi2Se3 of R-3m → C2/m → C2/c → I4/mmm phase under quasi-hydrostatic pressure condition and R-3m → C2/m → I4/mmm phase under nonhydrostatic pressure condition. The dynamic unstability and pressure condition sensitivity of C2/c phase may be account for the absence of C2/c phase in the phase transition sequence under nonhydrostatic pressure condition. Our findings obtain the high-pressure phase transition sequences of Bi2Se3 under hydrostatic and nonhydrostatic pressure condition, which can facilitate researchers to explore the novel properties in layered 3D topological insulators.

Pressure-Induced Evolution of Crystal and Electronic Structure of Ammonia Borane.

Ammonia borane (NH3BH3) has long attracted considerable interest for its high hydrogen content and easy dehydrogenation conditions which make it a promising hydrogen storage material. Here, we report on a computational study of the structural stability and phase transition sequence of NH3BH3 and associated lattice dynamics and electronic properties in a wide pressure range up to 300 GPa. The results confirm previously reported structures, including the experimentally observed orthorhombic Pmn21 structure at low temperature and ambient pressure, and predict the phase transition sequence Pmn21 → Pc → P21 → P1̅ for NH3BH3. Our calculations also reveal systematic trends of monotonically decreasing band gap with rising pressure in the three high-pressure NH3BH3 phases, which nevertheless all remain nonconducting up to the highest pressure of 300 GPa examined in this work. The present findings elucidate structural and electronic properties of NH3BH3 over an extensive pressure range, providing knowledge essential to further study of NH3BH3 in an expanded pressure-temperature phase space.

Site selective substitution of Eu3+ and its effects on structural and luminescent properties of monoclinic YP5O14 pentaphosphate

Y1-xEuxP5O14 (0 < x ≤ 1) pentaphosphate polycrystallines were synthesized by solid state reaction and the effects of Eu3+ content on the structure and luminescent properties were investigated. X-ray diffraction and Infrared spectroscopy studies revealed a sequence of the composition-driven structural phase transitions C2/c → P21/c; occur at the lower Eu3+ concentration (below 40 mol% of Eu3+ doping). The spectroscopic properties in UV-excitable range of the doped compounds were investigated. Site-selective laser excitation in the 5D2 level of Eu3+ ion was performed and luminescence decay times were measured at 30 K for 5 and 10%Eu3+ -doped YP5O14 samples. The obtained results clearly show that the Eu3+ ions are distributed over two distinct crystallographic sites. Careful analysis of the main 5D2→7FJ (J = 0, 2) transitions revealed a good agreement between the observed and expected components numbers for the local symmetry predicated upon the crystal structure of the monoclinic YP5O14. The spectroscopic results are discussed and correlated with the structural data.

Modification of the spectroscopic properties of Tb2O3 phosphor under the high-pressure phase transitions sequence

The high-pressure behavior of cubic Tb2O3 phase (C-type) has been investigated by in situ photoluminescence and Raman spectroscopy up to 18 GPa and 22 GPa, respectively. The luminescence spectrum of Tb2O3 at ambient conditions shows its characteristic sharp-line emission bands with the most intense one corresponding to the 5D4 - 7F5 transition, responsible for the green emission. Excitation and emission spectra measured at low temperature and at different emission and excitation wavelengths suggest that photoluminescence is governed by the Tb3+ in the non-centrosymmetric site (C2). A phase transition between 7.2 and 8.6 GPa is observed by Raman and photoluminescence experiments and is associated with a cubic-to-monoclinic (B-type) structural transformation. From 14 GPa the predominant modes in the Raman spectrum correspond to those from the trigonal phase (A-type), indicating that the pressure-induced structural phase transition sequence of Tb2O3 is C → B → A. Upon pressure release, the starting cubic phase is not recovered, but the monoclinic one.

Thermally-induced phase transitions in Pt/Tb/Fe trilayers

Structural phase formation induced by thermally-activated diffusion processes and intermixing of layered structures is a promising reaction pathway for the synthesis of unexpected (metastable) thin film materials. Furthermore, the sequence of structural phase transitions during annealing can substantially differ from those predicted by corresponding bulk phase diagrams due to the underlying grain boundary diffusion mechanisms as well as surface and interface effects. In this study, phase transitions in Pt/Tb/Fe trilayers occurring during post-annealing up to 620°C were investigated by various techniques including x-ray diffraction, transmission electron microscopy, secondary neutral mass spectrometry, Auger electron spectroscopy depth profiling, and magnetic properties measurements. At an annealing temperature of 215°C pronounced Pt and Tb diffusion intermixing is observed leading to the formation of the binary Pt2Tb phase. Further annealing up to 280 °C is accompanied by the appearance of the chemically disordered A1-FePt phase and significant Tb segregation to the outer surface forming an oxide layer. The chemically ordered L10-FePt phase starts to form in parallel to the disappearance of the Pt2Tb phase at 450°C. The final phase product at 620°C is characterized by the coexistence of two remaining phases, L10-FePt and TbO2. Structural phase transitions have a significant impact on the films magnetic properties – heat treatment leads to an enhancement of the coercive field. This fact is associated with the formation of the hard magnetic L10-FePt phase, which might be accompanied by grain isolation induced by partially Tb/Tb-O grain boundary filling.

Effects of crystal chemistry and local random fields on relaxor and piezoelectric behavior of lead-oxide perovskites

Random electric fields caused by the disordered distribution of heterovalent cations over the equivalent crystallographic positions are often considered to be the main reason of the relaxor behavior and the associated giant electromechanical response. Some models relate the development of the relaxor state to the crystal chemical properties of the constituent ions. In this work the functions of random fields and ferroactive cations are compared in perovskite solid solutions in the desirable for technological applications composition range of morphotropic phase boundary. The crystal structure, dielectric and ferroelectric properties, piezoelectric effect and electrostriction are investigated in technologically important ceramic solid solutions PbzBa1−z(Mg1/3Nb2/3)m(Zn1/3Nb2/3)y(Ni1/3Nb2/3)nTixO3 with substitutions in A (Pb2+ by Ba2+)- and B (Ti4+ by [B2+1/3Nb5+2/3]4+) perovskite sublattices. Two composition sections of the system are designed; in both of them the concentration of ferroactive ions, Pb2+ and Ti4+, respectively, varies within the same range of 15%, but the strength of quenched random electric fields changes significantly only in B-substituted ceramics. Similar behavior is found in both sections, including the same sequence of structural phase transitions and transformations from normal ferroelectric to relaxor state and similar evolution of properties with concentration. The results clearly demonstrate that the role of crystal chemical factors in the development of relaxor behavior and electromechanical performance of lead-oxide materials is not less important than that of quenched random fields. The mechanisms of the observed behavior are discussed in the frame of existing theoretical models.

Prediction and Synthesis of Dysprosium Hydride Phases at High Pressure.

Crystal structure prediction (CSP) methods recently proposed a series of new rare-earth (RE) hydrides at high pressures with novel crystal structures, unusual stoichiometries, and intriguing features such as high-Tc superconductivity. RE trihydrides (REH3) generally undergo a phase transition from ambient P63/mmc or P3̅c1 to Fm3̅m at high pressure. This cubic REH3 (Fm3̅m) was considered to be a precursor to further synthesize RE polyhydrides such as YH4, YH6, YH9, and CeH9 with higher hydrogen contents at higher pressures. However, the structural stability and equation of state (EOS) of any of the REH3 have not been fully investigated at sufficiently high pressures. This work presents high-pressure X-ray diffraction (XRD) measurements in a laser-heated diamond anvil cell up to 100 GPa and ab initio evolutionary CSP of stable phases of DyH3 up to 220 GPa. Experiments observed the Fm3̅m phase of DyH3 to be stable at pressures from 17 to 100 GPa and temperatures up to ∼2000 K. After complete decompression, the P3̅c1 and Fm3̅m phases of DyH3 recovered under ambient conditions. Our calculations predicted a series of phases for DyH3 at high pressures with the structural phase transition sequence P3̅c1 → Imm2 → Fm3̅m → Pnma → P63/mmc at 11, 35, 135, and 194 GPa, respectively. The predicted P3̅c1 and Fm3̅m phases are consistent with experimental observations. Furthermore, electronic band structure calculations were carried out for the predicted phases of DyH3, including the 4f states, within the DFT+U approach. The inclusion of 4f states shows significant changes in electronic properties, as more Dy d states cross the Fermi level and overlap with H 1s states. The structural phase transition from P3̅c1 to Fm3̅m observed in DyH3 is systematically compared with other REH3 compounds at high pressures. The phase transition pressure in REH3 shows an inverse relation with the ionic radius of RE atoms.

Polarized-light and electron microscopy study of the static domain structure of ferroic Fe3B7O13I boracite at room temperature

The static domain structure of ferroic Fe3B7O13I, (abbreviated as Fe-I) synthetic boracite crystals has been analyzed by polarized-light microscopy (PLM) and by field emission scanning electron microscopy (FE-SEM) at room temperature. As for most boracites, Fe-I shows dielectric, elastic, magnetic and optical properties of unusual interest. Upon cooling, Fe-I boracite shows a sequence of structural phase transitions from the cubic -43m to the orthorhombic mm2 (Tc = 348K), the monoclinic m (Tc = 218 K) and the trigonal 3m phases (Tc = 191 K). At room temperature, the Fe-I crystals present an orthorhombic domain structure which consists of six ferroic domains. Our results show that both techniques: PLM and FE-SEM are complementary for the visualization of ferroic domains.

Bond ordering and phase transitions in Na2IrO3 under high pressure

The Kitaev model of spin-1/2 on a honeycomb lattice supports degenerate topological ground states and may be useful in topological quantum computation. Na$_{2}$IrO$_{3}$ with honeycomb lattice of Ir ions have been extensively studied as candidates for the realization of the this model, due to the effective $J_{\text{eff}}=1/2$ low-energy excitations produced by spin-orbit and crystal-field effect. As the eventual realization of Kitaev model has remained evasive, it is highly desirable and challenging to tune the candidate materials toward such end. It is well known external pressure often leads to dramatic changes to the geometric and electronic structure of materials. In this work, the high pressure phase diagram of Na$_{2}$IrO$_{3}$ is examined by first-principles calculations. It is found that Na$_{2}$IrO$_{3}$ undergoes a sequence of structural and magnetic phase transitions, from the magnetically ordered phase with space group $C2/m$ to two bond-ordered non-magnetic phases. The low-energy excitations in these high-pressure phases can be well described by the $J_{\text{eff}}=1/2$ states.

The investigations of phase transitions in the (1-x)PbZrO3-xBiFeO3 nanocrystals using differential scanning calorimetry and Raman spectroscopy

Polycrystalline powders of PbZrO3, 0.98PbZrO3–0.02BiFeO3, and 0.96PbZrO3–0.04BiFeO3 were synthesised by means of a molten salt synthesis route. Their structure and morphology were studied using X-ray powder diffraction and scanning electron microscopy, respectively. The frequencies of the Raman lines were analysed and discussed in terms of the sequence of structural phase transitions. The measurements revealed the existence of a new intermediate phase observed below the Curie point (Tc) and an additional temperature anomaly above Tc, most likely connected with magnetic transition originating from BiFeO3 contribution. The addition of multiferroic BiFeO3 into the structure of antiferroelectric PbZrO3 suggests that the obtained solid solutions form multiferroic systems even at low BiFeO3 content. The Raman measurements were supplemented by dielectric studies and differential scanning calorimetry measurements. An excellent agreement for transition temperatures obtained by means of these three techniques suggests that BiFeO3 is uniformly distributed in the synthesised powder materials.

Efficient compression in color naming and its evolution

We derive a principled information-theoretic account of cross-language semantic variation. Specifically, we argue that languages efficiently compress ideas into words by optimizing the information bottleneck (IB) trade-off between the complexity and accuracy of the lexicon. We test this proposal in the domain of color naming and show that (i) color-naming systems across languages achieve near-optimal compression; (ii) small changes in a single trade-off parameter account to a large extent for observed cross-language variation; (iii) efficient IB color-naming systems exhibit soft rather than hard category boundaries and often leave large regions of color space inconsistently named, both of which phenomena are found empirically; and (iv) these IB systems evolve through a sequence of structural phase transitions, in a single process that captures key ideas associated with different accounts of color category evolution. These results suggest that a drive for information-theoretic efficiency may shape color-naming systems across languages. This principle is not specific to color, and so it may also apply to cross-language variation in other semantic domains.