Rhombohedral Perovskite Phase Research Articles

Electrical conductivity study of B-site Ga doped non-stoichiometric sodium bismuth titanate ceramics

The present investigation looks at the effect of Ga3+ doping for B-site Ti4+ on the phase stability and oxygen-ion conductivity of Na0.54Bi0.46TiO3-δ for the possible electrolyte application in low-temperature solid oxide fuel cells. Dense bulk samples were prepared using the conventional solid-state route. Although XRD revealed the presence of a single rhombohedral perovskite phase, SEM study indicated the existence of impurity phase in the form of fibers in the as-sintered samples. The local chemical compositional analysis showed Na/Bi molar ratio to be > 1 in the perovskite phase of all the tested compositions and the existence of Na2Ti6O13 compound in the impurity phase. Impedance spectroscopy studies suggested a monotonous decrease in bulk conductivity on Ga3+ doping on the B-site of Na0.54Bi0.46TiO3-δ. The bulk conductivity of 7.8 mS/cm measured in Na0.54Bi0.46TiO3-δ at 600 °C declined to 5.8 mS/cm on 2 at.% Ga3+ doping. The conductivity reduction was attributed to the formation of local defect clusters which act as sinks, and thus leads to decrease in the concentration of free oxygen vacancy. Although not much change in initial bulk conductivity of Na0.54Bi0.46Ti0.99Ga0.01O3-δ was found under various atmospheres from 500 °C to 600 °C, the annealing study carried out at 600 °C for 12 h under 5% H2–95% N2 condition showed the decomposition of perovskite phase to form metallic Bi. Both pure and Ga-doped samples showed a considerable conductivity degradation of 12% after 100 h ageing in air at 600 °C. The phenomenon related to the formation of local defect clusters over time was proposed to be a possible reason for the observed conductivity decay.

Structural and dielectric studies of excessive Bi3+ containing perovskite PZT and pyrochlore biphasic ceramics

The influence of high concentration of Bi3+ substitution on the phase formation, microstructure, dielectric and conductivity properties of lead zirconate titanate (Pb1−xBi2x/3(Zr0.5Ti0.5O3) with x = 0.1, 0.2, 0.3 and 0.4)) (PBZT) ceramics synthesized by a high energy ball milling method, has been studied. X-ray diffraction analysis showed that the samples have crystallized to rhombohedral or tetragonal perovskite phases depending on the concentration of Bi3+ substitution. As x is increased to more than 0.1 mol% the presence of a pyrochlore phase, identified as Bi2Ti2O7, has also been observed. The crystalline and prismatic nature of the grains improved as Bi3+ concentration is increased. Dielectric studies revealed that all the samples are characterized by high values of ε′ and as Bi3+ concentration is increased Tc values are found to decrease from 450 °C to 395 °C. The DC electrical conductivity studies showed the existence of both positive and negative temperature coefficient of resistance (PTCR and NTCR) in the present systems indicating their potential applications in switching devices.

Role of morphological characteristics on the conductive behavior of LaNiO3 thin films

LaNiO3 (LNO) thin films were synthesized via the polymeric precursor method and sintered using conventional and microwave heating sources. The samples were characterized by structural morphological and electrical techniques. The crystalline structure was analyzed by X-ray diffraction and indicated rhombohedral perovskite phase in both films sintered using conventional and microwave heating. The films morphology was evaluated by scanning and transmission electron microscopy, and atomic force microscopy, and the results point out that microwave heating exerts direct influence on the morphological characteristics of LNO films contributing towards the change in the grain size distribution, porosity and roughness. Conductivity was also investigated through four-probe measurements, which pointed out a conductive and ohmic behavior of the LNO thin films prepared via the polymeric precursor method where a direct relationship was found between the morphological characteristics and the electrical properties of LNO film.

The Role of Oxygen Partial Pressure in Controlling the Phase Composition of La1−x Sr x Co y Fe1−y O3−δ Oxygen Transport Membranes Manufactured by Means of Plasma Spray-Physical Vapor Deposition

La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) deposited on a metallic porous support by plasma spray-physical vapor deposition is a promising candidate for oxygen-permeation membranes. Ionic transport properties are regarded to depend on the fraction of perovskite phase present in the membrane. However, during processing, the LSCF powder decomposes into perovskite and secondary phases. In order to improve the ionic transport properties of the membranes, spraying was carried out at different oxygen partial pressures p(O2). It was found that coatings deposited at lower and higher oxygen partial pressures consist of 70% cubic/26% rhombohedral and 61% cubic/35% rhombohedral perovskite phases, respectively. During annealing, the formation of non-perovskite phases is driven by oxygen non-stoichiometry. The amount of oxygen added during spraying can be used to increase the perovskite phase fraction and suppress the formation of non-perovskite phases.

Effect of annealing atmosphere on the structural and electrical properties of BiFeO3 multiferroic ceramics prepared by sol–gel and spark plasma sintering techniques

Phase-pure BiFeO3 powders were synthesized by sol–gel technique. Based on these powders, high-density BiFeO3 ceramics were prepared by spark plasma sintering (SPS) at 700°C along with annealing for 2 and 4h, respectively, at 650°C under atmospheres of air and oxygen. X-ray diffraction analysis revealed that the 4h-oxygen-annealed sample contained a single rhombohedral perovskite phase while the samples annealed in the other conditions contained small quantities of impurity phases besides the rhombohedral perovskite phase. The relative density of the 4h-oxygen-annealed sample was about 96%, being apparently higher than that of the other samples. In comparison with the 4h-air-annealed sample, the dielectric constant of the 4h-oxygen-annealed sample was relatively higher. The activation energy for electrical conduction was about 1.17eV for the 4h-oxygen-annealed sample while it was about 0.98eV for the 4h-air-annealed sample, showing that the former would have a lower room-temperature conductivity (~2.6×10−14Scm−1) than the latter (~2.1×10−13Scm−1). It is therefore anticipated that the oxygen-annealed sample could possess better ferroelectric properties as compared to the air-annealed sample.

Synthesis and Characterization of BNT Thin Films Prepared by Sol-gel Method

Polycrystalline piezoelectric lead-free Bi0.5Na0.5TiO3 (abbreviated as BNT) thin films were deposited on Pt/TiO2/SiO2/Si substrates by an optimized Sol-Gel process. The phase structure and morphology of the as-prepared product were examined by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The film treated at 700°C with the rapid thermal processor (RTP) for 30sec is dense and well crystallized in the rhombohedral perovskite phase. The dielectric constant and loss tangent at 10kHz are 420 and 0.07%, respectively, while the remnant polarization and coercive field are 12μC/cm2 and 120kV/cm, respectively, at 1000Hz.

Low-temperature solution-combustion synthesis and magneto-structural characterization of polycrystalline La1–x Ag y MnO3 (y ≤ x) manganites

Silver is known to be a highly mobile (low-soluble) component in Ag-doped perovskite manganites and hence several non-perovskite phases can exist in silver doped manganite perovskites with most synthetic routes making its synthesis to be problematic. In search of soft synthesis route, the low temperature combustion synthesis and magneto-structural studies of polycrystalline La1–xAgyMnO3 (y ≤ x) ceramic manganites using glycine as a fuel is reported. The sintered powders were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDAX) analysis, Thermo Gravimetric Analysis (TGA) and Vibrating Scanning Magnetometer (VSM) measurements. XRD patterns showed formation of mainly single rhombohedral perovskite phase for the La0.8Ag0.15MnO3 sample and an admixture of secondary phases with La0.8Ag0.1MnO3 and La0.8Ag0.2MnO3 samples. The distinct microstructure and higher magnetic properties observed for La0.8Ag0.15MnO3 sample compared to the other samples were discussed based on the XRD results.

Relaxor Behavior and Dielectric Relaxation in Lead-Free Solid Solutions of (1 − x)(Bi0.5Na0.5TiO3)–x(SrNb2O6)

Lead-free compositions (1 − x) (Bi0.5Na0.5TiO3)–x(SrNb2O6) (BNT-SN) are synthesized by a simple solid state reaction route. SN diffuse in distorted perovskite BNT for low concentrations of SN (x ≤ 0.03) and are stabilized in rhombohedral perovskite phase with experimentally observed relative density of the ceramics >92%. A temperature-dependent dielectric response exhibits a broad dielectric peak that shows frequency-dependent shifts towards higher temperatures reflecting typical relaxor behavior. Modified Curie–Weiss law and Lorentz-type empirical relationships are used to fit the dielectric data that exhibit almost complete diffuse phase transition characteristics. In addition, significant dielectric dispersion is observed in a low-frequency regime in both components of the dielectric response and a small dielectric relaxation peak is observed. Cole–Cole plots indicate the poly-dispersive nature of the dielectric relaxation.

Structural and electrical characterizations of BiFeO3 capacitors deposited by sol–gel dip coating technique

Bismuth ferrite (BiFeO3) thin films were deposited by sol–gel dip coating (SGDC) technique on Si-P(100) and glass substrates to investigate the structural and electrical characteristics. The aluminum (Al) metal contacts were formed on the samples deposited on the Si-P(100) to fabricate metal-oxide-semiconductor (MOS) capacitors. The fabricated MOS structures were characterized electrically by capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. The structural characterizations were performed by X-ray diffraction technique and scanning electron microscopy. The compositions of the films were investigated by energy-dispersive X-ray spectroscopy. The results exhibit that pure rhombohedral perovskite phase films were fabricated without any elemental contamination. Average grain sizes of the BiFeO3 deposited on silicon and glass wafers were found to be about 34,50 and 30,00nm, respectively. In addition, while the thin films deposited on glass substrate exhibit porous surface, those deposited on Si-P(100) wafers exhibit dense microstructure with a homogenous surface. Moreover, the C–V and G/ω–V characteristics are sensitive to applied voltage frequency due to frequency dependent charges (Nss) and series resistance (Rs). The peak values of Rs have been decreased from 2,6kΩ to 40Ω, while Nss is varied from 6,57×1012 to 3,68×1012eV−1cm−2 with increasing in frequency. Consequently, pure phase polycrystalline BiFeO3 thin films were fabricated successfully by SGDC technique and BiFeO3 dielectric layer exhibits stable insulation characteristics.

Effect of A and B-site substitution with Pb, La and Ti on phase stabilization and multiferroic properties of BiFeO3

The work presents a comparative study of the effects of divalent (Pb), trivalent (La) and tetravalent (Ti) substituents on the multiferroic properties of BiFeO3 (BFO). Both A and B-sites were substituted to obtain the compositions i.e. (Bi1−x−yLaxPby)(Fe1−zTiz)O3 (x, y=0, 0.1, 0.2 and z=0, 0.05, 0.1, 0.15). Each of the substituent was particularly chosen i.e. Pb was chosen to keep the lone pair character which is the similar case as Bi ion. Additionally isovalent La was chosen to achieve single phase by reducing Bi volatization. Both these ions, on substitution, stabilized the crystal structure and suppressed the formation of extra phases which are unavoidable in pure BFO. All the Ti substituted and Bi0.8La0.2FeO3 compositions exhibited rhombohedral perovskite (R3c) phase, while Bi0.8Pb0.2FeO3 and Bi0.8La0.1Pb0.1FeO3 exhibited cubic phase. Mössbauer measurements revealed that impurity phase in case of compositions with divalent and trivalent substituents, disappeared completely when Ti substituted Fe. For all the compositions Fe ions were found in +3 state. High temperature dielectric properties showed that all the compositions were ferroelectric with paraelectric transition lying well above the room temperature. Weak ferromagnetism was found in Ti substituted compositions where coercivity was found to increase as the Ti concentration increases. All the BFO samples substituted with Pb, exhibited a dielectric anomaly in the temperature range, 100°C⩽T⩽250°C. A systematic reduction in the intensity of the dielectric anomaly peak was observed as a function of Ti concentration which indicates that the anomaly is related to the conductivity and is element specific. However, Mössbauer data revealed absence of Fe2+ state, which ensured that it was not related with the presence of Fe2+ ions. Saturation polarization was found to increase as Ti concentration increased from 0% to 10%.

Synthesis and study of structural, magnetic and microwave absorption properties in multiferroic BiFeO3 electroceramic

Phase pure nano-sized BiFeO3 (BFO) has been successfully prepared by citrate based sol–gel method. X-ray diffraction study revealed the formation of pure and well-crystallized BiFeO3 nano-crystallites in a rhombohedral perovskite phase for the samples sintered at 600 °C. The examination of microstructure showed uniform hexagonal shaped grains. From magnetisation measurement, it was observed that an increase in sintering temperature from 600 to 700 °C decreased the remanent magnetization from 0.025 to 0.003 emu/g suggesting a weak ferromagnetic nature at room temperature. Moreover, better microwave absorption properties with minimum reflection loss were also observed. Impedance measurements were performed by vector network analyser in frequency range 8.2–12.4 GHz for the sample annealed at 700 °C. From the dielectric permittivity (e = e′ − je″) and magnetic permeability (µ = µ′ − jµ″) measurements, it was found that the observed dielectric and magnetic losses were higher in the case of BFO sintered at 700 °C.

Enhanced piezoelectric properties of BaZrO3-substituted 0.67BiFeO3-0.33BaTiO3 lead-free ceramics

Lead-free ceramics with compositions of (1−x)[0.67Bi1.05FeO3-0.33BaTiO3]-xBaZrO3 (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) [BF-BT-BZx] have been prepared through a conventional solid-state reaction method. The effects of BZ substitution on the crystal structural, microstructural, piezoelectric, and electrical properties of the ceramics were investigated. The X-ray diffraction patterns revealed that all ceramics were formed with a mixed structure of rhombohedral and tetragonal perovskite phases. For x = 0.03, good ferroelectric and piezoelectric properties were observed: 2P r = 43 μC/cm2 and 2E c = 61 kV/cm. The static- and dynamic-piezoelectric constants were observed to be 52 pC/N and 330 pm/V, respectively.

Influence of fuel on morphology of LSM powders obtained by solution combustion synthesis

Combustion synthesis is a simple and reproducible method used to obtain fine ceramic powders, which can be used in energy-generation devices such as solid oxide fuel cells (SOFCs). Strontium-doped lanthanum manganites (LSM) are materials applied commonly as cathodes in a SOFC and can be obtained by combustion synthesis. Different combustion synthesis routes of LSM were evaluated in this paper, considering the influence of fuel amount and type in the phase formation and morphology of the powders. Moreover, a new fuel mixture, urea and sucrose, was proposed for the preparation of LSM powders. The synthesized powders showed significant loss of mass when obtained with 200% excess of oxidizers, and the use of urea resulted in single-phase powders directly from the combustion reaction. After calcination, a single-phase rhombohedral perovskite phase was identified in all powders. A larger specific surface area of calcined powders (34.9m2/g) and a smaller crystallite (sized 18nm) were obtained using sucrose as fuel, followed by the synthesis with mixed fuels (13.2m2/g and 26nm). These results were correlated with the morphology of the aggregates, which was visibly influenced by the nature of the precursor solution. The mixed fuels combustion led to a powder where the particles aggregated in a form of submicrometric hollow structures.

Effects of Fe2O3 addition on the piezoelectric and the dielectric properties of 0.99Pb(Zr0.53Ti0.47)O3-0.01Bi(Y1−x Fe x )O3 ceramics for energy-harvesting devices

The 0.99Pb(Zr0.53Ti0.47)O3-0.01Bi(Y1−x Fe x )O3 [PZT-BYF(x)] (x = 0.0 − 0.6) piezoelectric ceramics have been synthesized by using a modified conventional solid-state method. Initially, the perovskite Pb(Zr0.53Ti0.47)O3 (PZT) and the cubic-phase Bi(Y1−x Fe x )O3 [BYF(x)] were presynthesized and mixed to prepare PZT-BYF(x) ceramic composites. The effects of BYF(x) addition on the phase formation, microstructure, and piezoelectric/dielectric properties were measured as functions of sintering temperature. In addition to these measurements, the piezoelectric voltage constant (g 33) and the piezoelectric transduction coefficient (d 33 × g 33) were measured in order to evaluate the essential criteria for an energy-harvesting material. For all the specimens, X-ray diffraction analyses showed a complete solid solution with co-existing tetragonal and rhombohedral perovskite phases. All the ceramics exhibited denser and finer microstructures, which produced a high relative density of ≥ 98%. Scanning electron microscopy (SEM) observations revealed that BYF(x) addition enhanced the sintering density through the formation of a liquid phase. The doping with BYF(x) in the PZT system was found to be effective for maintaining a high Curie temperature of around 377–390 °C. With increasing content of Fe2O3 in the BYF(x) system, the piezoelectric and the dielectric properties were significantly improved. At a sintering temperature of 1170 °C, the piezoelectric and the dielectric properties of PZT-BYF(x) ceramics showed desirable values; this resulted in a significantly higher transduction coefficient. The compositions of PZTBYF(0.1), PZT-BYF(0.2), and PZT-BYF(0.3) showed a considerably lower e 33 T value, but higher d 33 and k p values. Therefore, within the concentration limit of x = 0.1 to 0.3 moles of Fe2O3, the g 33 and the d 33 × g 33 values were improved significantly (g 33 > 53 × 10−3 Vm/N and d 33 × g 33 > 20000 m2/N). The maximum transduction coefficient of 20167 × 10−15 m2/N was obtained from the composition of PZT-BYF(0.3). The high values of g 33 and d 33 × g 33 make these piezoelectric ceramics potential candidates for applications in energy-harvesting devices.

New Electrode of La0.75Sr0.25Mn0.5Cr0.5-XCuxO3-δ (x=0, 0.05, 0.10, 0.20) for Symmetric Solid Oxide Fuel Cell

: New perovskite oxides La0.75Sr0.25Mn0.5Cr0.5-x Cu x O3-δ (LSMCr0.5-x Cu x , x=0, 0.05, 0.10, 0.20) have been developed as both cathode and anode for symmetric single solid oxide fuel cells (SOFCs). The as-prepared LSMCr0.5-x Cu x powders are rhombohedral perovskite phase, and their properties are remarkably affected by Cu content (x). For example, the particle sizes and electrical conductivities of LSMCr0.5-x Cu x increase with x both in air and in 5% H2-Ar atmosphere. Their p-type conductivity shows lower values under 5% H2-Ar reducing atmosphere than in air due to the decrease of the ratio of Mn4+/Mn3+ cation pairs through the reduction of Mn4+. Among of the oxides, LSMCr0.45Cu0.05 shows the best anodic and cathodic performance in symmetrical half cells. The maximum power density of a LSMCr0.45Cu0.05 / ScSZ / LSMCr0.45Cu0.05 symmetric single SOFC reaches as high as 451.2 mW·cm-2 in wet H2 as fuel at 900 oC. Keywords : solid oxide fuel cell; symmetric cell; LSCM; Cu substitution Acknowledgements: This research was financially supported by the Natural Science Foundation of China (21173147), 973 Program of China (2014CB239700). Thanks were also given to the support of National Key Laboratory of Metallic Matrix Composite Material.*Corresponding author. Tel.: +86 21 34206255; Fax: +86 21 54741297.E-mail address: yimei@sjtu.edu.cn (Y.-M. Yin).

Ho and Ti co-doped BiFeO3 multiferroic ceramics with enhanced magnetization and ultrahigh electrical resistivity

Bi0.9Ho0.1Fe0.95O3 and Bi0.9Ho0.1Fe0.9Ti0.05O3 ceramics were prepared and compared to reveal the effects of Ho and Ti codoping in BiFeO3. X-ray diffraction indicated that both ceramics had a high rhombohedral perovskite phase content, and microstructural analyses showed that the grains of the Bi0.9Ho0.1Fe0.9Ti0.05O3 ceramics were much smaller than those of Bi0.9Ho0.1Fe0.95O3. An electrical resistivity of more than 1 × 1014 Ω · cm at room temperature, and a magnetic hysteresis loop with a remnant magnetization 2Mr of ∼ 0.485 emu/g were obtained for Bi0.9Ho0.1Fe0.9T0.05O3; both were much higher than those of Bi0.9Ho0.1Fe0.95O3. Changes in the defect subsystem of BiFeO3 induced by Fe-deficiency and (Ho,Ti) codoping are proposed as being responsible for the improvement in the properties.

Effect of Sintering Time on Dielectric and Piezoelectric Properties of Lanthanum Doped Pb(Ni1/3Sb2/3)-PbZrTiO3 Ferroelectric Ceramics

produce electrical output in response to ambient pressures, vibrations, movements etc. In the present studies, sintering time for composition Pb0.98La0.02(NiSb)0.05[(Zr0.52Ti0.48)0.995]0.95O3 (La-PNS-PZT) was optimised to achieve properties suitable for power harvesting. Composition was processed through mixed oxide route and sintered at 1270 °C for 20 min, 40 min, 60 min, 80min and 100 min. XRD pattern indicated the presence of both, ferroelectric tetragonal and ferroelectric rhombohedral perovskite phases. The optical photographs shown the uniform and dense microstructure for the samples sintered for 60 min, resulted into optimum piezoelectric charge coefficient, voltage coefficient, electromechanical coupling coefficient and figure of merit. Power harvesting capabilities in response to impact of stainless steel ball (8.25 gm) from 150 mm height were evaluated and compared with PZT type 5A. La-PNS-PZT produced batter electrical output (5.11 W, 71.13 μJ) across the matching load resistance of 4000 Ω and 2.08 W maximum power and 20.79 μJ energy by PZT type 5A disc across the matching load resistance of 1000 Ω. Defence Science Journal, 2013, 63(4), pp.418 -422 , DOI:http://dx.doi.org/10.14429/dsj.63.4866

The Effect of Firing Temperatures on (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 Ceramics Prepared via the Combustion Technique

The (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 (PBZT) ceramics were prepared via the combustion technique. (CO(NH2)2) was used as a fuel. The effect of firing temperature on PBZT's phase formation, microstructure and electrical properties were investigated. The calcination and sintering temperatures were 600°C–1000°C and 1100°C–1300°C. The pure rhombohedral perovskite was obtained from the powders calcined at 850°C. The average particle size tended to increase with increased calcination temperatures. A pure rhombohedral perovskite phase was found in all pellet samples. The average grain size and linear shrinkage tended to increase from 0.57 to 2.15 μm and from 6.8 to 15.8% with increased sintering temperatures. The dielectric results indicated the relaxer behavior of PBZT ceramics. The Curie temperature tended to decrease with increasing sintering temperatures. The highest density (∼7.39 g/cm3) and highest dielectric constant (∼8620) were obtained by using the combustion technique which was higher than the conventional mixed oxide method.

Fabrication of 0.62[0.75PMN-0.25PYbN]-0.38PT Ceramics Using One Step Calcination via Combustion Technique

The fabrication of 0.62[0.75Pb(Mg1/3Nb2/3)O3-0.25Pb(Yb1/2Nb1/2)O3]-0.38PbTiO3 ceramics (abbreviated PMN-PYbN-PT) by combustion technique using one step calcination was studied. Glycine was used as fuel to reduce the reaction temperature. The phase formation, microstructure, density and dielectric properties were investigated. It was shown that calcination method is more effective than conventional solid state reaction. The crystal structure of PMN-PYbN-PT ceramics exhibited a single rhombohedral perovskite phase in samples sintered at temperature T < 1200°C. The pyrochlore phase was found in the samples sintered at 1200°C. The average grain size of the ceramics increases with increasing sintering temperature. The density and the maximum dielectric constant increases with increasing sintering temperatures up to 1150°C, and then decreases at higher temperatures. The maximum density (8.04 g/cm3), highest dielectric constant (19000) and excellent ferroelectric properties (Pr ∼ 41.05 μC/cm2and Ec ∼ 8.1 kV/cm) were obtained for the sample sintered at 1150°C.

Effects of Doped AE (Ca, Sr) on Synthesis and Structure of Lanthanum Chromite-Based Nano-Powder

Using sol-gel method, a series of nanocrystalline materials La1-xAExCrO3(AE=Ca, Sr) were synthesized. Difference between Ca- and Sr-doped lanthanum chromites were investigated by carrying out differential scanning calorimetry (DSC), thermogravimetric analysis (TG), X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM). It was found that the synthesis temperature (1-xCaxCrO3, and CaCrO4as the second phase (x≥0.2) at the room temperature. LSC is composed of single orthorhombic perovskite phase for x=0.1, while the orthorhombic and rhombohedral perovskite phases coexist for x=0.2, and only rhombohedral perovskite phase for x=0.3. Further studies showed that the maximum solubility of Sr was lower than that of Ca in lanthanum chromite.