Morphotropic Transformation Research Articles

Full quasi-system “from LaF3 to LuF3” as a combination of 14 binary systems of lanthanide trifluorides with maximal chemical proximity

The combination of 15 RF3 (R – rare earth elements – REEs without ScF3 and YF3) into one system “from LaF3 to LuF3” we call a full quasi-system (QS). It consists of 14 serially linked particular systems (PartSs): LaF3–CeF3; CeF3-PrF3; PrF3-NdF3; NdF3-PmF3; PmF3-SmF3; SmF3-EuF3; EuF3-GdF3; GdF3-TbF3; TbF3-DyF3; DyF3-HoF3; HoF3-ErF3; ErF3–TmF3; TmF3-YbF3; YbF3-LuF3. The atomic numbers (Z) of cations from 57 (La) to 71 (Lu) and the temperature (T) are axies of QS. The conditions of including RF3 in PartSs is the neighborhood of R (Ln - lanthanides) positions in Periodic Table of Chemical Elements and |ΔZ| ​= ​1. This securities of maximum chemical proximity (СhProx) of RF3's components. The QS obeys the phase rule, principles of continuity and conformity. Full QS contains all signs of chemical RF3's interactions identified in 34 studied LnF3-Ln’F3 systems. These signs are dependent of ΔZ: perfect and limited isomorphism and two varieties (peritectic and eutectic) of structural true morphotropic transformations (MTs) of phases. Modifications of LnF3 forms the solid solutions (ss) Ln1-xLn'xF3 with average Zav=(1-x)NLn ​+ ​x(N+1)Ln’ (N from 57 to 71). These ss reveal the lanthanide contraction (LC) in the regions |ΔZav|<1. Full QS is an individual sub-level of chemical classification of LnF3-Ln’F3 systems. It is a tool for studies the chemical interactions LnF3, analyzing fine consequences of LC, creating a special system of Ln3+ ionic radii for LnF3, studies of density anomalies (negative thermal expansion), prediction of phase diagrams unexplored systems RF3-R’F3 and other problems of rare earth trifluorides chemical family.

Spontaneous polarization and DC resistivity investigations in Ba[1.6-(3x/2)]Sr2.4ErxNa1.4Li0.6Nb10O30 tungsten bronze structured nano-phased relaxor ferroelectrics

Spontaneous polarization and DC resistivity investigations in Er+3 doped nano-structured relaxor ferroelectrics, viz., Ba[1.6-(3x/2)]Sr2.4ErxNa1.4Li0.6Nb10O30 for x in the range of 0–1 with 0.1 step are reported. Spontaneous polarization and remnant polarization exhibit enhancement with Er doping. For x equal to 0.1 normal ferroelectric behaviour observed. For x equal to 0.2 and 0.3, relaxor nature with low Pr value observed. A transition from normal FE relaxor to a linear dielectric behaviour is observed with doping. Smeared dielectric anomaly addressed by subtle morphotropic transformation from commensurate to incommensurate phases. Er content with x equal to 0.2 and 0.3 exposed to 20KV/cm vouched greater charge storage, slim hysteresis and low coercive field. Overall decreasing trend of polarization for 0.4 < x < 1.0 inferred resumption of paraelectric behaviour with doping due to induced defects and electron traps. Reduced ferroelectric response with increasing Er3+ doping is addressed by decreasing particle/grain size. Distinct slopes of resistivity plots vouched for low temperature PTCR, and medium or high temperature NTC behaviour. At low temperatures, the vacancies at grain boundaries exhibit diffusion. For medium temperatures, hybrid transport mechanism contributed by electrons and defects proposed. At higher temperatures, polaron hopping process takes lead to realize super-Para-Electric (SPE) behavior. Heterogeneous electric profiles and striations result for diffused DC resistivity and mediated by compensation of global charge by local charge. NTC behaviour in medium and high temperature regions addressed by diversity of potential barrier and conductivity paths across the grain boundaries. Er doping for BSNN resulted for distinct PTC, relaxor and NTC behavior. NTC behaviour in higher temperatures is attributed to eventual release of charge carriers from the Oxygen vacancies. Low ranged activation energy Ea due to relaxing behavior of charge carriers involves mobile dipoles, holes or defects with deep acceptor traps. Relatively lower activation energies by Er+3 doping at low and medium temperatures are indirectly tuned by Oxygen ion vacancies and entangled dipoles, while the latter get freed at higher temperatures to exhibit Super Para Electric behaviour.

High-temperature chemistry of Y, La and lanthanide trifluorides in RF3–R’F3 systems. Part 3. Phase composition of the studied systems

The phase composition of 34 ​T-x RF3–R’F3 systems of trifluorides of rare-earth elements (R-REE) is described. The isomorphism of REE ions in three types of RF3 structures has been quantitatively characterized. The growth of the difference of atomic numbers ΔZ ​= ​|Z(R)–Z(R′)| of the REE limits isomorphism by morphotropic transformations (MTs) of solid solutions (ss). The studied systems show phase reactions of MT: peritectic (MT-I) and eutectic (MT-II). MTs are invariant phase reactions of the two ss with the melt. MT express high-temperature chemical interactions of RF3. The parameters MT (TMT and x) were determined for 11 ​MT-I and 13 ​MT-II. As a result of MT, the following phases are formed: 16 ​t-ss (LaF3 type); 24 β-ss (β-YF3 type), and 16 α-ss (α-YF3 type). The compositions of all detected phases are given in the chemical equations of phase reactions. The prospects of using R1-xR’xF3 crystals for photonics and ionics of solids are considered.

Polymorphism, Isomorphism, and Morphotropy in Trifluorides of Rare-Earth Elements (R) and RF3–R'F3 Systems

The relationship between the polymorphism, isomorphism, and morphotropy has been traced for the homologous series of 16 trifluorides of rare-earth elements (REEs) (without ScF3) and R1 – xR $$_{x}^{'}$$ F3 phases (R is an REE) based on the T–x diagrams of RF3–R'F3 systems. The polymorphism is determined by the REE atomic numbers Z and Т values, which change the cation/anion radius ratio r+/r–. Four structural RF3 subgroups are selected according to the polymorphism and types of LaF3, β-YF3, and α-YF3 (α-UO3) structures: A (R = La–Nd), B (R = Pm–Gd), C (R = Tb–Ho), and D (R = Er–Lu, Y). Combinations of RF3 form 10 types of RF3–R’F3 systems. Isomorphism (both perfect and limited) manifests itself in the homogeneity range of R1 – xR $$_{x}^{'}$$ F3 phases. It affects the R1 – xR $$_{x}^{'}$$ F3 structure via the r+/r– ratio by preparing (jointly with Т) their morphotropic transformations (MTs). The morphotropy of R1 – xR $$_{x}^{'}$$ F3 is regulated by the parameters Т and х via the ratio r+/r– and is implemented by means of phase reactions of melt with R1 – xR $$_{x}^{'}$$ F3 and R1 – yR $$_{y}^{'}$$ F3 of different structures at peritectic (MT-I) and (or) eutectic (MT-II) temperatures. Morphotropic transformations of R1 – xR $$_{x}^{'}$$ F3 structures occur at the boundary of GdF3–TbF3 (Z = 64.43–64.51; МT-I; 1186 ± 10°С) and HoF3–ErF3 (Z = 67.67–67.36; МT-II; 1120 ± 10°С). A definition of true morphotropy for systems in T–x coordinates is given.

Sm6-xMoO12-δ (x = 0, 0.5) and Sm6WO12 – Mixed electron-proton conducting materials

Samarium molybdates Sm6-xMoO12-δ (x=0, 0.5) and samarium tungstate Sm6WO12 – potential mixed electron-proton conductors have been studied by X-ray diffraction, Raman spectroscopy, SEM and impedance spectroscopy (in ambient air and in dry and wet air).Solid solutions differing in structure have been obtained in the Sm2O3-MoO3 system at 1600°C. The samarium molybdate Sm6MoO12 has the fluorite structure (Fm¯3m). The less samarium rich solid solution Sm5.5MoO11.25 crystallizes in a rhombohedral (R3¯) structure. The morphotropic transformation is due to the change in the chemical composition of the solid solution with decreasing Sm3+ concentration. The total conductivity of the cubic fluorite phase Sm6MoO12 at 750°C in air (1.48×10−3S/cm, Ea=1.22eV) is an order of magnitude higher than that of rhombohedral Sm5.5MoO11.25 (2.34×10−4S/cm, Ea=1.11eV). At low temperatures (T<500°C), the Arrhenius plot of total conductivity for Sm6MoO12 and Sm5.5MoO11.25 in air deviates from linearity, suggesting that there is a proton contribution to its conductivity at these temperatures, like in the case of the Sm5.4Zr0.6MoO12.3 zirconium-doped molybdate. Below ~500°C, Sm6MoO12 fluorite and fluorite-like Sm6WO12 have identical Arrhenius plots of conductivity in ambient air.The region of dominant proton conductivity is wider for Sm6WO12 than Sm6MoO12, reaching temperatures as high as 750°С for the former. The absolute values of total conductivity obtained for samarium tungstate and molybdate at 400°С in wet air are virtually identical and close to 3×10−6S/cm, which suggests the conductivity of both compounds is dominated by protons at low temperatures and the proton transport numbers are similar.

Room-temperature multiferroic responses arising from 1D phase modulation in correlated Aurivillius-type layer structures

Structural instability induced by chemical substitution in multiferroic materials, especially in layer-structured oxides of the Bi4Ti3O12–BiFeO3 system, gives rise to intriguing phenomena and extraordinary coupling properties. In this work, we carefully studied an analogous morphotropic structural transformation in Co-substituted Bi7Ti3Fe3O21 oxides, similar to a morphotropic phase boundary. Large effects (including ferroelectric, dielectric and ferromagnetic) and abnormal magnetic behaviour were recorded at the analogous morphotropic transformation region (AMTR). 1D phase-modulated structures composed of two different layered phases and structural distortions inside the AMTR were visualized. Analyses of the correlations between oxygen octahedral distortions and multiferroic responses confirmed that the enhanced multiferroic responses inside the AMTR are intrinsic to the 1D correlated interface structures, mainly arising from such structural distortions due to the existence of different lattice strains and the change of crystal symmetry.

Nanoscale structural modulation and enhanced room-temperature multiferroic properties.

Availability of a single-phase multiferroic material functional at room temperature poses a big challenge, although it is very important to both fundamental physics and application development. Recently, layered Aurivillius oxide materials, one of the most promising candidates, have attracted considerable interest. In this work, we investigated the nanoscale structural evolution of the six-layer Bi7Fe(3-x)Co(x)Ti3O21 when substituting excessive Co. Nanoscale structural modulation (NSM) occurred at the boundaries when changing the material gradually from the originally designed six-layer nanoscale architecture down to five and then four, when increasing the Co content, inducing a previously unidentified analogous morphotropic transformation (AMT) effect. The AMT's net contribution to the enhanced intrinsic multiferroic properties at room temperature was confirmed by quantifying and deducting the contribution from the existing impurity phase using derivative thermo-magneto-gravimetry measurements (DTMG). Significantly, this new AMT effect may be caused by a possible coupling contribution from co-existing NSM phases, indicating a potential method for realizing multiferroic materials that function at room temperature.

Synthesis and crystal structure of gold–silver sulfoselenides: morphotropy in the Ag3Au(Se,S)2 series

Gold–silver sulfoselenides of Ag3Au(Se,S)2 series—Ag3AuSe1.5S0.5, Ag3AuSeS, and Ag3AuSe0.5S1.5—have been synthesized by fusing the elements in the required stoichiometric amounts in evacuated quartz ampoules. The single crystal X-ray diffraction data indicate the existence of two solid-solution series: petzite-type cubic Ag3AuSe2—Ag3AuSeS (space group I4132) and trigonal Ag3AuSe0.5S1.5—Ag3AuS2 (space group $$ R\overline{3} c $$ ). Both crystal structures differ in the distribution of Ag+/Au+ cations in the same distorted body-centered cubic sublattice of chalcogen anions. The morphotropic transformation results from the shrinkage of anion packing accompanied by the shortening of Ag–Ag distances. The structure of uytenbogaardtite mineral, earlier incorrectly interpreted as a tetragonal or cubic cell, is similar to that of the trigonal Ag3AuS2 end-member.

Solid solutions of the PbII(M1−x M x ′)IVO3 (M, M′=Ti, V and Cr) perovskites, synthesized under high pressure and high temperature

The structural characteristics of Pb(M1−x M)O3 solid solutions, with M, M′=Ti, V and Cr, have been investigated by powder X-ray diffraction. The specimens studied were synthesized under high pressure and high temperature in a ‘belt-type’ apparatus. The analogy between polymorphic, compared with the PbTiO3 (tetragonal↔cubic phase transition), and morphotropic transformation in these systems is sufficiently close so as to be able to use the Birch–Murnaghan equation of state of PbTiO3 and relate it to the internal (or the so-called ‘chemical’) pressure generated by the substitution of vanadium or chromium along the different solid solutions.

Theoretical approach to reconstructive and morphotropic phase transitions

Abstract The basic concepts of the phenomenological approach to reconstructive transitions are illustrated by a working example, and their specific properties are outlined. A theoretical approach to morphotropic transformations, which are transitions between phases with different stoichiometries, is introduced through the description of the vanadium-oxide system.

Theory of morphotropic transformations in vanadium oxides

A theory of the morphotropic transformations occurring between stoichiometric phases in the vanadium-oxide system is proposed. The interconnections between the different structures are shown to result from definite symmetry-breaking mechanisms from a common parent structure. The homologous series ${\mathrm{V}}_{n}{\mathrm{O}}_{2n\ensuremath{-}1}$ and ${\mathrm{V}}_{n}{\mathrm{O}}_{2n+1}$ are interpreted as sequences of lock-in commensurate phases. Identification of the order-parameter symmetries provides us with the form of the thermodynamic functions which allow for construction of the theoretical phase diagrams in which the different phases are inserted. The general procedure allowing for the description of morphotropic transformations is outlined.

Mechanism of the morphotropic transformation between the rutile and corundum structural types.

The rutile/corundum structural transformation which is based on crystallographic shear is discussed in terms of a one-dimensional disorder model. The transformation process is described by a simple model based on the structural relationship between the rutile-type and corundum-type phases. The model is able to handle randomly spaced crystallographic shear planes, the so-called Wadsley defects, as well as clustered CS planes. Calculations hsow that simply modifying the probability parameters of the model can lead to phase segregation. X-ray powder diffraction patterns are calculated for the proposed transformation mechanism as a function of the stoichiometry x in MO(2-x) in order to show the influence of such defects on the intensities and linewidths of the Bragg reflections.

Temperature-Dependent Elastic Constants and Dielectric Properties of (Zn1 – xCdx)3(P1 – yAsy)2 Crystals

Crystals of constant-lattice-parameter (a ≃ const) and constant-thermal-expansion (α a ≃ const) (Zn1 – xCd x )3(P1 – yAs y )2 solid solutions with 0.71 ≤ x ≤ 0.94 and 0.2 ≤ y ≤ 1 are prepared, and their elastic and dielectric properties are studied between 78 and 400 K. The elastic constants are found to decrease linearly with increasing temperature and to rise monotonically with increasing Cd and As content, up to x = 0.94 and y = 1. These findings are interpreted in terms of structural changes and bond rearrangement near the morphotropic structural transformation. Dielectric permittivity rises monotonically with temperature and solute concentration and shows a sharp upturn at x = 0.94 andy = 1. The extremely high dielectric permittivity is interpreted in terms of charge transfer between defect complexes responsible for deep levels in the band gap.

スカンジウムニオブ酸鉛‐チタン酸鉛‐ジルコン酸鉛セラミックスの作製と電気的性質

Solid solution ceramics of the system xPb(Sc1/2Nb1/2)O3-yPbTiO3-zPbZrO3, where x=0-0.4, y=0.3-0.6, z=0-0.7, x+y+z=1, were prepared by the solid state reaction of powder materials. The density, dielectric and piezoelectric properties and crystal structures of sintered body were studied. The system was composed of three crystal phases at room temperature: the tetragonal, rhombohedral and orthorhombic. Sintering of the system xPb(Sc1/2Nb1/2)O3-yPbTiO3-zPbZrO3 was much easier than that of each terminal compositions, and well sintered ceramics were obtained for the composition near the morphotropic transformation.Piezoelectric ceramics with high dielectric constants and high radial coupling coefficient, kr, and low mechanical quality factor were obtained for the compositions near the morphotropic transformation. Pb(Sc1/2Nb1/2)0.3Ti0.44Zr0.26O3 ceramics showed the high kr of 0.67.

イッテルビウムニオブ酸鉛‐チタン酸鉛‐ジルコン酸鉛セラミックスの作製と電気的性質

Solid solution ceramics of the system xPb (Yb1/2Nb1/2) O3-yPbTiO3-zPbZrO3, where x=0.1-0.7, y=0.2-0.7, z=0.1-0.7, and x+y+z=1, were prepared by the solid state reaction of powder materials. Ceramic, dielectric and piezoelectric properties and crystal structures of the system were studied. The system is composed of three crystal phases at room temperature: the monoclinic, tetragonal and rhombohedral. Sintering of the system xPb (Yb1/2Nb1/2) O3-yPbTiO3-zPbZrO3 is much easier than that of each terminal compositions and well sintered ceramics were obtained for the compositions near the morphotropic transformation. Piezoelectric ceramics with high dielectric constants and high radial coupling coefficient, kr, and low mechanical quality factor were obtained for the compositions near the morphotropic transformation. The composition Pb (Yb1/2Nb1/2)0.1Ti0.5Zr0.4O3 showed the highest kr of 0.46.

リチウムニオブ酸鉛‐チタン酸鉛‐ジルコン酸鉛系磁器の相転移と電気的性質

Solid solution ceramics in the system xPb(Li1/4Nb3/4)O3-yPbTiO3-zPbZrO3 were prepared by the solid state reaction of powder materials. The ceramic, dielectric, and piezoelectric properties and crystal structures of the products were studied. The compositions within the ternary system were sintered much more easily than the end compositions, and a well sintered high density ceramics was obtained for the compositions near the morphotropic transformation. Piezoelectric ceramics with high relative dielectric constants, high radial coupling coefficient and low resonant resistance were obtained for the composition near the morphotropic transformation. The composition Pb(Li1/4Nb3/4)0.2Ti0.4Zr0.4O3 showed the highest radial coupling coefficient.

Electric Properties of Pb(Sb1/2Nb1/2)O3–PbTiO3–PbZrO3 Ceramics

Solid-solution ceramics of ternary system xPb(Sb1/2Nb1/2)O3– yPbTiO3– zPbZrO3 were prepared by the solid-state reaction of powder materials. Ceramic, electric, dielectric and piezoelectric properties and crystal structures of the system were studied. Sintering of the system xPb(Sb1/2Nb1/2)O3– yPbTiO3– zPbZrO3 is much easier than that of each end composition, and well-sintered high-density ceramics were obtained for the compositions near the morphotropic transformation. Piezoelectric ceramics with high relative dielectric constants, high radial coupling coefficient and low resonant resistance were obtained for the composition near the morphotropic transformation. The composition Pb(Sb1/2Nb1/2)0.075Ti0.45Zr0.475O3 showed the highest dielectric constant (εr=1690), and the composition Pb(Sb1/2Nb1/2)0.05Ti0.45Zr0.5O3 showed the highest radial coupling coefficient (kp=64%).

マグネシウムタンタル酸鉛‐チタン酸鉛‐ジルコン酸鉛系磁器の相転移と電気的性質

Solid solution ceramics of the system xPb(Mg1/3Ta2/3)O3-yPbTiO3-zPbZrO3 were prepared by the solid state reaction of powder materials. Ceramic, dielectric, and piezoelectric properties and crystal structures of the system were studied. The system is composed of four crystal phases at room temperature: the cubic, pseudocubic, tetragonal, and rhombohedral. Sintering of the system xPb(Mg1/3Ta2/3)O3-yPbTiO3-zPbZrO3 is much easier than that of each end compositions and a well sintered high density ceramics was obtained for the compositions near the morphotropic transformation. Piezoelectric ceramics with high relative dielectric constants and high radial coupling coefficient and low resonant resistance were obtained for the composition near the morphotropic transformation. The composition Pb(Mg1/3Ta2i3)0.125-Ti0.435Zr0.44O3 showed the highest radial coupling coefficient.

Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3—PbTiO3—PbZrO3 Solid Solution Ceramics

Ceramic and electrical properties and crystal structures of the system Pb(Mgl/3Nb2/3‐ PbTiO3‐PbZrO3 are described. The system is composed of three crystal phases at room temperature: pseudocubic, tetragonal, and rhombohedral. A high dielectric constant and radial coupling coefficient and low resonant resistance were obtained for the compositions near the morphotropic transformation. The composition Pb(Mgl/3Nb2/3)0.4375Ti0.4375Zr0.125O3 had the lowest temperature coefficient of resonant frequency.