Solid Solution Limit Research Articles

Quasi-ternary system CuGaS2–CuInS2–2CdS

Abstract The quasi-ternary CuGaS 2 –CuInS 2 –2CdS system was investigated using differential-thermal analysis and phase X-ray diffraction. Isothermal section of the system at 870 K and projection of the liquidus surface were constructed. Limits of the boundary solid solutions were determined.

Mineralogical and chemical characteristics of some natural jarosites

This paper presents a detailed study of the mineralogical, microscopic, thermal, and spectral characteristics of jarosite and natrojarosite minerals. Systematic mineralogic and chemical examination of a suite of 32 natural stoichiometric jarosite and natrojarosite samples from diverse supergene and hydrothermal environments indicates that there is only limited solid solution between Na and K at low temperatures, which suggests the presence of a solvus in the jarosite-natrojarosite system at temperatures below about 140 °C. The samples examined in this study consist of either end members or coexisting end-member pairs of jarosite and natrojarosite. Quantitative electron-probe microanalysis data for several natural hydrothermal samples show only end-member compositions for individual grains or zones, and no detectable alkali-site deficiencies, which indicates that there is no hydronium substitution within the analytical uncertainty of the method. In addition, there is no evidence of Fe deficiencies in the natural hydrothermal samples. Hydronium-bearing jarosite was detected in only one relatively young supergene sample suggesting that terrestrial hydronium-bearing jarosites generally are unstable over geologic timescales. Unit-cell parameters of the 20 natural stoichiometric jarosites and 12 natural stoichiometric natrojarosites examined in this study have distinct and narrow ranges in the a- and c-cell dimensions. There is no overlap of these parameters at the 1 σ level for the two end-member compositions. Several hydrothermal samples consist of fine-scale (2–10 μm) intimate intergrowths of jarosite and natrojarosite, which could have resulted from solid-state diffusion segregation or growth zoning due to variations in the Na/K activity ratio of hydrothermal solutions.

Indium and gallium oxynitrides prepared in the presence of Zn 2+ by ammonolysis of the oxide precursors obtained via the citrate route

Ammonia nitridation of indium and gallium oxide precursors obtained through a soft solution route led to their oxynitrides [In 0.97□ 0.03][N 0.92O 0.08] at 660 °C and [Ga 0.89□ 0.11][N 0.66O 0.34] at 850 °C, respectively, where □ refers to a In or Ga vacancy. Cation vacancies in their wurtzite-type lattice were eliminated in similar preparations with the co-presence of Zn 2+ by forming complete solid solutions of (InN) 1− x (ZnO) x and (GaN) 1− y (ZnO) y . The optical absorption edge shape was found to be relatively steep at the solid solution limits of x ≈ 0.23 and y ≈ 0.33 compared to the case without zinc.

Hexaferrites and phase relations in the iron-rich part of the system Sr–La–Co–Fe–O

The iron rich part of the system was examined in the temperature range of 1200–1380 °C in air, with focus on the solid solutions of M-type hexaferrites. Samples of suitable compositions were studied by electronprobe microanalysis (EPMA). Substituted Sr-hexaferrites in the system Sr–La–Co–Fe–O do not follow the 1:1 substitution mechanism of La/Co in M-type ferrites. Due to the presence and limited Co 2+-incorporation Fe 3+-ions are reduced to Fe 2+ within the crystal lattice to obtain charge balance. In all examined M-type ferrites divalent iron is formed, even at 1200 °C. The substitution principle Sr 2++Fe 3+↔La 3++(Fe 2+, Co 2+) yields to the general substitution formula for the M-type hexaferrite Sr 2 + 1 - x La 3 + x Fe 2 + x - y Co 2 + y Fe 3 + 12 - x O 19 (0≤ x≤1 and 0≤ y≤ x). In addition Sr/La-perovskite SS ( SS=solid solution), Co/Fe-spinel SS, hematite and magnetite are formed. Sr-hexaferrite exhibits at 1200 °C a limited solid solution with small amounts of Fe 2+ (SrFe 12O 19↔Sr 0.3La 0.7Co 0.5Fe 2+ 0.2Fe 11.3O 19). At 1300 and 1380 °C a continuous solid solution series of the M-type hexaferrite is stable. SrFe 12O 19 and LaCo 0.4Fe 2+ 0.6Fe 11O 19 are the end members at 1300 °C. The maximum Fe 2+O content is about 13 mol% in the M-type ferrite at 1380 °C (LaCo 0.1Fe 2+ 0.9Fe 11O 19).

Electrical conduction behavior of La, Co co-doped SrTiO3 perovskite as anode material for solid oxide fuel cells

Abstract The effects of La- and Co-doping into SrTiO 3 perovskite oxides on their phase structure, electrical conductivity, ionic conductivity and oxygen vacancy concentration have been investigated. The solid solution limits of La in La x Sr 1 − x TiO 3 − δ and Co in La 0.3 Sr 0.7 Co y Ti 1 − y O 3 − δ are about 40 mol% and 7 mol%, respectively, at 1500 °C. The incorporation of La decreases the band gap and thus increases the electrical conductivity of SrTiO 3 remarkably. La 0.3 Sr 0.7 TiO 3 − δ shows an electrical conductivity of 247 S/cm at 700 °C. Co-doping into La 0.3 Sr 0.7 TiO 3 − δ increases the oxygen vacancy concentration and decreases the migration energy for oxygen ions, leading to a significant increase in ionic conductivity but at the expense of some electrical conductivity. The electrical and ionic conductivities of La 0.3 Sr 0.7 Co 0.07 Ti 0.93 O 3 − δ are 63 S/cm and 6 × 10 −3 S/cm, respectively, at 700 °C. Both La 0.3 Sr 0.7 TiO 3 − δ and La 0.3 Sr 0.7 Co 0.07 Ti 0.93 O 3 − δ show relatively stable electrical conductivities under oxygen partial pressure of 10 −14 –10 −19 atm at 800 °C. These properties make La 0.3 Sr 0.7 Co 0.07 Ti 0.93 O 3 − δ a promising anode candidate for solid oxide fuel cells.

Comparative study of Li[Co 1− zAl z]O 2 prepared by solid-state and co-precipitation methods

Li[Co 1− z Al z ]O 2 (0 ≤ z ≤ 0.5) samples were prepared by co-precipitation and solid-state methods. The lattice constants varied smoothly with z for the co-precipitated samples but deviated for the solid-state samples above z = 0.2. The solid-state method may not produce materials with a uniform cation distribution when the aluminum content is large or when the duration of heating is too brief. Non-stoichiometric Li x [Co 0.9Al 0.1]O 2 samples were synthesized by the co-precipitation method at various nominal compositions x = Li/(Co + Al) = 0.95, 1.0, 1.1, 1.2, 1.3. XRD patterns of the Li x [Co 0.9Al 0.1]O 2 samples suggest the solid solution limit is between Li/(Co + Al) = 1.1 and 1.2. Electrochemical studies of the Li[Co 1− z Al z ]O 2 samples were used to measure the rate of capacity reduction with Al content, found to be about −250 ± 30 (mAh/g)/( z = 1). Literature work on Li[Ni 1/3Mn 1/3Co 1/3− z Al z ]O 2, Li[Ni 1− z Al z ]O 2 and Li[Mn 2− y Al y ]O 4 demonstrates the same rate of capacity reduction with Al/(Al + M) ratio. These studies serve as baseline characterization of samples to be used to determine the impact of Al content on the thermal stability of delithiated Li[Co 1− z Al z ]O 2 in electrolyte.

Phase equilibria in the quasi-ternary system Ag 2S–In 2S 3–CdS at 870 K

An isothermal section of the quasi-ternary system Ag 2S–CdS–In 2S 3 at 870 K was investigated using X-ray phase analysis. No quaternary intermediate phase was found. A continuous solid solution series between In 2S 3, AgIn 5S 8 and CdIn 2S 4 was discovered; a limited solid solution range of CdS is localized along the AgInS 2–CdS section.

The phase relations in the Gd–Fe–Ga ternary system at 500 °C

The isothermal section (500 °C) of the phase diagram of the Gd–Fe–Ga ternary system was investigated by X-ray powder diffraction analysis. Eleven binary compounds, GdGa 2, GdGa, Gd 3Ga 2, Gd 5Ga 3, GdFe 2, GdFe 3, Gd 2Fe 17, Fe 3Ga, Fe 6Ga 5, Fe 3Ga 4 and FeGa 3, have been confirmed. Two ternary compounds, GdFe 5.3Ga 6.7 and GdFe 5Ga 7, were found in this ternary system at 500 °C. The compound GdFe 5.3Ga 6.7 is orthorhombic ScFe 6Ga 6-type structure (space group Immm) with a = 0.8567 (9), b = 0.86960 (9) and c = 0.50782 (5) nm, while the compound GdFe 5Ga 7 is tetragonal ThMn 12-type structure (space group I4/ mmm) with a = 0.8651(1) and c = 0.50934 (6) nm. The isothermal section at 500 °C consists of 16 single-phase regions, 31 two-phase regions and 16 three-phase regions. The maximum solid solubilities of Ga in GdFe 2, GdFe 3, Gd 2Fe 17 are 9.2, 9.0, and 44.3 at.% respectively. The homogeneity range of GdGa 2 is from 22 to 33.3 at.% Ga in Gd–Ga side but the solid solubility of Fe in this compound is very small. The homogeneity range of GdFe 5Ga 7 is from 53.8 to 59.2 at.% Ga. Very limited solid solutions were measured in the other compounds.

Synthesis and structural mechanisms of the 2201-type ferrites and polytypes: Fe 2(Sr 2 − xA x)FeO 6.5 − δ/2 (A = Ba, La, Tl, Pb and Bi)

The Fe 2(Sr 2 − x A x )FeO 6.5 − δ/2 systems have been investigated, by doping the iron rich 2201-type parent structure with Ba 2+, La 3+ and 5d 10 post-transition cations. The syntheses have been carried out up to the limit of the 2201-type solid solutions, in order to test the role of the double iron layer Fe 2O 2.5 − δ/2 . The localisation of the charge carriers in these compounds is consistent with their strong antiferro-magnetism. The investigation was then carried out in the transition part of the diagram up to the formation of stable phases. The study of structural mechanisms was carried using high resolution electron microscopy (transmission and scanning transmission), electron diffraction and energy dispersive spectroscopy. Different non-stoichiometry mechanisms are observed, depending on the electronic structure and chemical properties of the doping elements. The specific behavior of the modulated double iron layer is discussed.

Conductivity of SnP 2O 7 and In-doped SnP 2O 7 prepared by an aqueous solution method

SnP 2O 7 and In-doped SnP 2O 7 have been prepared by an aqueous solution method using (NH 4) 2HPO 4 as phosphorous source. It was found that the solid solution limit in Sn 1 − x In x (P 2O 7) 1 − δ was at least x = 0.12. All pyrophosphates in the Sn 1 − x In x (P 2O 7) 1 − δ ( x ≤ 0.12) series exhibit 3 × 3 × 3 superlattice structures. The conductivities of Sn 0.92In 0.08(P 2O 7) 1 − δ in air are 6.5 × 10 − 6 and 8.0 × 10 − 9 S/cm at 900 and 400 °C, respectively, when prepared by an aqueous solution method and annealed at 1000 °C. The conductivity of undoped SnP 2O 7 is slightly lower. However, it was also found that the low-temperature conductivities of pyrophosphates annealed only at 650 °C are several orders of magnitude higher than those annealed at 1000 °C, which could be related to a trace amount of an amorphous secondary phase. The peak conductivity was in this case observed at around 250 °C, which is the same temperature as previously observed in In-doped SnP 2O 7 although the conductivity is still three orders of magnitude lower in the present study. These differences can be related to large differences in particle size and morphology, and all in all, the conductivities of SnP 2O 7-based materials are very sensitive to the synthetic history.

Lanthanum pyrochlores and the effect of yttrium addition in the systems La 2−xY xZr 2O 7 and La 2−xY xHf 2O 7

The crystal structures of the compounds La 2− x Y x Zr 2O 7 and La 2− x Y x Hf 2O 7 with x=0.0, 0.4, 0.8, 1.2, 1.6, and 2.0 have been studied using neutron powder diffraction and electron microscopy to determine the stability fields of the pyrochlore and fluorite solid solutions. The limits of pyrochlore stability in these solid solutions are found to be close to La 0.8Y 1.2Zr 2O 7 and La 0.4Y 1.6Hf 2O 7, respectively. In both systems the unit cell parameter is found to vary linearly with Y content across those compositions where the pyrochlore phase is stable, as does the x-coordinate of the oxygen atoms on the 48 f ( x, 3 8 , 3 8 ) sites. In both systems, linear extrapolations of the pyrochlore data suggest that the disordering is accompanied by a small decrease in the lattice parameter of approximately 0.4%. After the pyrochlore solid solution limit is reached, a sharp change is observed from x∼0.41 to 0.375 as the disordered defect fluorite structure is favoured. Electron diffraction patterns illustrate that some short-range order remains in the disordered defect fluorite phases.

Lithium ion conductivity of LiLaO2-Li2ZrO3 solid solutions

The limits of the LiLaO2-and Li2ZrO3-based solid solutions in the LiLaO2-Li2ZrO3 system have been determined: 0–10 mol % Li2ZrO3 and 0–5 mol % LiLaO2, respectively. We have studied the transport properties (electronic conductivity, temperature and composition dependences of conductivity and activation energy) of lithium lanthanate and the solid solutions in the LiLaO2-Li2ZrO3 system. Conduction in LiLaO2 is likely due to lithium ion transport through a polyhedral network.

Reaction-sintering of lead-free piezoceramic compositions: (0.95 − x)Na0.5K0.5NbO3–0.05LiTaO3–xLiSbO3

Incorporation of LiSbO3 into the lead-free piezoceramic composition 0.95Na0.5K0.5NbO3–0.05LiTaO3 produced a change from an orthorhombic to tetragonal crystal system in samples produced by reaction-sintering. The inferred limit of solid solution along the compositional join, (0.95 − x)Na0.5K0.5NbO3–0.05LiTaO3–xLiSbO3, occurred at x ~ 0.06. Differential scanning calorimetry indicated broad peaks at temperatures associated with ferroelectric–paraelectric transitions. The transition temperatures decreased with increasing values of x, up to x = 0.06. Microstructures showed secondary grain growth; a slight decrease in grain-size with increasing LiSbO3 modification was identified.

Preparation of Barium Titanate–Potassium Niobate Solid Solution System Ceramics and Their Piezoelectric Properties

Barium titanate (BaTiO3, BT)–potassium niobate (KNbO3, KN) solid solution system ceramics were prepared by normal sintering, and their piezoelectric properties were measured. The phase diagram of the BT–KN system was investigated by dielectric measurement and X-ray diffraction (XRD). The Curie temperature (TC) was almost constant at approximately 130 and 430 °C for ceramics with KN contents below and above 50 mol %, respectively. At room temperature, two phases, ferroelectric tetragonal and ferroelectric orthorhombic, coexisted in the composition range from 0.7BT–0.3KN to 0.1BT–0.9KN. This system was found to be a limited solid solution system that involves BT- and KN-rich phases. Their piezoelectric properties were investigated on the basis of the electric-field dependence of strain measurements. For ceramics with KN contents below 30 mol %, the apparent piezoelectric constant (d33) decreased approximately with increasing KN content, whereas above 30 mol %, the apparent d33 increased as a function of KN content.

Controllable thermal expansion and phase transition in Yb 2− xCr xMo 3O 12

The thermal expansion and phase transition of solid solutions Yb 2− x Cr x Mo 3O 12 have been investigated by X-ray powder diffraction and differential thermal analysis. The XRD patterns and the results of Rietveld refinement of Yb 2− x Cr x Mo 3O 12 indicate that the solid solution limit was in the composition range of 0.0 ≤ x ≤ 0.4 and 1.7 ≤ x ≤ 2.0. Yb 2− x Cr x Mo 3O 12 (0.0 ≤ x ≤ 0.4) has an orthorhombic structure and exhibits negative thermal expansion between 200 °C and 800 °C. Yb 2− x Cr x Mo 3O 12 (1.7 ≤ x ≤ 2.0) crystallizes in monoclinic below the phase transition and above, transforms to orthorhombic. Both monoclinic and orthorhombic compounds Yb 2− x Cr x Mo 3O 12 (1.7 ≤ x ≤ 2.0) present positive thermal expansion. Orthorhombic Yb 2− x Cr x Mo 3O 12 exhibit anisotropic thermal expansion with the contraction of a and c axes, and the linear thermal expansion coefficients range from negative to positive with increasing chromium content. Partial substitution of Yb 3+ for Cr 3+ exhibits depressed monoclinic to orthorhombic phase transition.

Crystal growth and piezoelectricity of BaTiO3–CaTiO3 solid solution

We report the crystal growth and piezoelectric properties of (1−x)BaTiO3–xCaTiO3. It is found that the perovskite structure is facilitated by incorporating small Ca into Ba site and single crystals for a wide composition range of 0.02⩽x⩽0.34 can be grown by the floating zone technique with a high rate of 20mm∕h. High values of piezoelectric coefficient (d33=180–310pC∕N) have been demonstrated for the single crystals as well as the biphasic polycrystals with composition close to the solid solution limit. These findings may stimulate further interests in the developments of lead-free piezoelectrics or optical devices.

Microstructure and microwave dielectric properties of Ba 5Nb 4O 15–BaWO 4 composite ceramics

Microwave dielectric composite ceramics with compositions of (1 − x)Ba 5Nb 4O 15– xBaWO 4 ( x = 0–1) were prepared by firing the mixture of Ba 5Nb 4O 15 and BaWO 4. The sintering temperature of the composite ceramics was reduced from 1400 to 1100 °C with increasing BaWO 4 content. XRD patterns indicate that Ba 5Nb 4O 15 and BaWO 4 coexisted and no secondary phase was detected in sintered bodies. The composite ceramics have the finer grained microstructure compared with the pure Ba 5Nb 4O 15 ceramics. TEM observation and EDS analysis reveal that a very thin interfacial area (∼60 nm in width) was formed due to the limited solid solution between Ba 5Nb 4O 15 and BaWO 4 grains. With increasing BaWO 4 (from x = 0 to x = 0.65), the dielectric constants ( ɛ r) and the temperature coefficient of resonant frequency ( τ f) of the ceramics decrease from 39.2 to 16.9 and from +78 to −4.3 ppm/°C, respectively, while the quality factors ( Q × f value) increase from 26,000 to 56,700 GHz. The samples with x = 0.54–0.65 sintered at 1100 °C exhibit good microwave dielectric properties: ɛ r = 21.0–16.9, Q × f = 49,500–56,700 GHz, and τ f = 8.9–−4.3 ppm/°C.

Crystal structure and dielectric properties of Ca0.85Nd0.1TiO3 - LnAIO3 ceramics

The microwave dielectric properties of Ca(0.85)Nd(0.1)TiO(3) - LnAlO(3) (Ln = Sm, Gd, Dy, Er) ceramics are investigated in this paper. The structural characteristics of the specimens were evaluated by Rietveld refinement of Xray diffraction (XRD) patterns and high-resolution transmission electron microscopy (HRTEM). Solid solution limits were dependent on the ionic radius of Ln(3+) ions. With the decrease of the ionic radius of the Ln(3+) ions, the thermal stability of the resonant frequency decreases. This can be attributed to the increased level of oxygen octahedral distortion caused by the increase in the B-site bond valence in the ABO(3) perovskite structure. The dielectric constant (K) and the quality factor (Qf) of the specimens were dependent on the polarizability and grain size, respectively.

Chemical synthesis, structural elucidation and quantum-chemical modeling of a [formula omitted] doped gallium oxynitride prepared by precursor nitridation

Chromium doped gallium oxynitrides having the wurtzite structure were prepared by ammonia nitridation of oxide precursors derived via the citrate route. The solid solution limits of less than 1 at.% Cr 3+ were confirmed by both XRD and EXAFS on the nitrided product at 750 ∘C in the wurtzite-type crystal lattice. The doped product was paramagnetic with a small amount of an antiferromagnetic impurity, but there was no ferromagnetic interaction among the doped Cr 3+ ions in the gallium oxynitride. Density-functional electronic structure calculations on the basis of a wurtzite-type supercell containing 194 atoms reveal the oxynitride material to be metastable, and confirm the presence of spin-polarized Cr 3+ cations located exactly on former Ga 3+ tetrahedral sites.

The appearance of an orthorhombic BIMEVOX phase in the system Bi 2Mg xV 1 − xO 5.5 − 3 x/2 − δ at high values of x

The structural and electrical behaviour of an orthorhombic BIMEVOX phase Bi 2Mg 0.3V 0.7O 5.395 − δ is discussed. This composition lies close to the BIMEVOX solid solution limit in the pseudo-binary system Bi 2MgO 4–Bi 2VO 5.5 − δ . Unlike most other BIMEVOXes, the BIMGVOX system exhibits an orthorhombic polymorph above the composition limit for stabilisation of the tetragonal γ-phase. On heating, Bi 2Mg 0.3V 0.7O 5.395 − δ exhibits phase separation at around 650 °C, which is reversed at 840 °C. On cooling, the BIMEVOX phase is maintained throughout to room temperature. Small changes in structure and conductivity are evident between 500 and 700 °C and suggest a structural and or compositional change in the vandate layer of the BIMEVOX phase at these temperatures.