Nanostructured perovskite oxides – LaMO3 (M=Al,Co, Fe) prepared by co-precipitation method and their ethanol-sensing characteristics

Nanostructured La-based perovskite oxides − LaMO₃ (M=Al, Co, Fe) were synthesized by a new co-precipitation procedure using metal nitrate and carbonate salts as starting materials. X-ray diffraction and energy dispersive X-ray spectroscopic results confirmed the formation of single-phase nanocrystalline perovskite oxides with high purity. Characterizations by scanning/transmission electron microscopy and nitrogen adsorption revealed that LaAlO₃ was produced in the form of rectangular porous nanorods exhibiting much larger surface area and porosity compared with densely aggregated LaCoO₃ particles and loosely clustered LaFeO₃ nanoparticles with cracked-egg morphologies. The materials were characterized for gas sensing towards ethanol at 200–350 °C. From gas-sensing results, the LaAlO₃ sensor displayed n-type gas-sensing behaviors with considerably higher ethanol response than p-type LaFeO₃ and LaCoO₃ sensors, respectively. In particular, the LaAlO₃ sensor exhibited a high response of 16.45–1000 ppm ethanol and excellent ethanol selectivity against NO₂, SO₂, CO and H₂ at 350 °C. The superior gas-sensing performances could be attributed to the effective receptor function, transducer function and utility factor of LaAlO₃ nanorod structures prepared by the co-precipitation method.     

The nature of active sites for the oxidation of methane on La-based perovskites

Highly crystalline, monophasic LaFeO₃ and LaCoO₃ perovskites, prepared by the explosion method, are shown to be heterogeneous at surface level. The outmost atomic layers of these perovskites contain high concentrations of carbonate-type species. Their specific activities for methane combustion are in fact identical to La₂O₂CO₃ and air-exposed La₂O₃. These results compared with pertinent data from the literature hint that surface heterogeneity may be often present in mixed oxides catalysts.     

LaFeO3 ceramics as selective oxygen sensors at mild temperature

In this study, an investigation about the oxygen sensing properties of lanthanum orthoferrite (LaFeO₃) ceramics is reported. LaFeO₃ nanoparticles were synthesized by using tartaric sol-gel route and annealed in air at different temperatures (500, 700 and 900 °C). The samples have been characterized by using thermal analysis (TA), BET surface area and porosity, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results of sensing tests indicate that LaFeO₃ nanoparticles exhibit good response to oxygen at mild temperatures (300–450 °C). The effect of annealing temperature on gas sensing performance was investigated, demonstrating that LaFeO₃ ceramics obtained after annealing at 500 °C display better characteristics with respect to others. The oxygen sensor developed shows also high stability in humid environment and excellent selectivity to oxygen over other interfering gases such as CO, NO₂, CO₂, H₂ and ethanol.     

Phase equilibria in the La2O3-Y2O3-Nd2O3 system at 1500 °C

The phase equilibria in the ternary La₂O₃-Y₂O₃-Nd₂O₃ system at 1500 °C were studied by X-ray diffraction, petrography, and electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcination at 1100 and 1500 °C. The solid solutions based on various polymorphous forms of source components and ordered phase of LaYO₃ were revealed in the system. The isothermal section of the phase diagram for the La₂O₃-Y₂O₃-Nd₂O₃ system has been developed. It was established that in the ternary La₂O₃-Y₂O₃-Nd₂O₃ system there exist fields of solid solutions based on hexagonal (A) and monoclinic (B) modifications of La₂O₃ and Nd₂O₃, cubic (C) modification of Y₂O₃, as well as perovskite-type structure of LaYO₃ (R) with rhombic distortions. The systematic study that covered the whole composition range excluded the formation of new phases. The refined lattice parameter of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.     

Fuel Gas Upgrading Over La1−xCexCoO3 Mixed Oxide with Toluene as Model Compound

Perovskite-type mixed oxides La_1?xCe_xCoO₃ (x = 0, 0.2, 0.4) were synthesized by sol–gel method via polyvinyl alcohol (PVA) as gelating agent. LaCoO₃ and CeO₂ phases were presented while intermediate phase, La(OH)₃, disappeared during LaCoO₃ transformation. Introduction of Ce decreased crystal size of catalyst from 22.18 to 13.38 nm. Particle size and specific surface area were in the range of 9.58–13.72 μm and 6.03–9.23 m²/g, respectively. The addition of Ce increased the reduction temperature which indicated the strong interaction between Co and perovskite structure. Catalytic activity was investigated by steam reforming of toluene at 500–800 °C. Conversions of carbon and hydrogen to CO, H₂, and CH₄ at steam per carbon ratio (S/C) of 2:1 were clearly higher than 4:1. Increasing S/C ratio to 4:1 inhibited syngas production efficiency by combustion and water–gas shift reaction. The presence of Ce in the catalyst did not improve activity of catalyst significantly. However the metal enhanced stability by promoting the formation of filamentous carbon on the surface such that the active sites are still accessible to the active gas during the experiment. After reforming, catalysts were transformed to La(OH)₃, Co⁰, and Ce₄O₇ phases and no significant deterioration in catalytic performance was detected after 6 h. In this study steam reforming of toluene over La_0.6Ce_0.4CoO₃ at 800 °C with S/C 2:1 yielded highest carbon conversion as CO and hydrogen conversion as H₂ of 64.42 and 63.23 %. The LHV and H₂/CO of produced gas at this optimum condition are 4.22 MJ/N m² and 2.91, respectively.     

Sintering of LaCoO3 based ceramics

The densification, microstructure and phase evolution of near stoichiometric, Co-excess and Co-deficient perovskite La_1−xM_xCoO_3−δ (M=Ca, Sr; x=0, 0.2) powders have been investigated by electron microscopy and powder X-ray diffraction. Sub-micron powders were prepared from nitrate precursors using the glycin-nitrate and the EDTA methods. The sintering temperature was observed to decrease with Ca or Sr substitution. Dense materials with grain size in the order of 3–5 μm have been obtained at 1200°C for near stoichiometric powders. Considerable grain growth was observed at higher sintering temperatures. The presence of other crystalline phases in addition to the perovskite due to Co-excess/-deficiency considerably affects the microstructure and acts as grain growth inhibitors by grain boundary pinning. The volume fraction of secondary phases is particularly large in the case of Co-deficient LaCoO₃ due to the formation of La₄Co₃O₁₀. In non-stoichiometric La_0.8Ca_0.2CoO₃, a liquid phase consisting mainly of CaO and CoO was observed at 1400°C causing exaggerated grain growth. Considerable pore coarsening was observed in Co-excess La_0.8Ca_0.2CoO₃ at 1350°C. The present investigation demonstrates the importance of controlling the stoichiometry of LaCoO₃ based ceramics in order to obtain dense materials with well defined microstructure.     

Phase equilibrium in binary La2O3-Dy2O3 and ternary CeO2-La2O3-Dy2O3 systems

Cerium oxide doped with oxides of rare earth elements is a multifunctional material, a wide range of uses which is associated with its unique physicochemical properties. Phase diagrams of multicomponent systems are the physicochemical basis for the creation of new materials with improved characteristics.In this work, phase equilibria in ternary CeO₂–La₂O₃–Dy₂O₃ and binary La₂O₃–Dy₂O₃ systems in the whole concentration range were studied. No new phases have been identified in these systems. An isothermal section of the phase diagram of the CeO₂–La₂O₃–Dy₂O₃ system at a temperature of 1500 °С is constructed. No new phases have been detected in the system. It was found that in the studied ternary system solid solutions are formed on the basis of (F) modification of CeO₂ with structure of fluorite type, monoclinic (B), cubic (C) and hexagonal (A) modifications of Ln₂O₃.In the La₂O₃–Dy₂O₃ binary system (1500–1100 °С) three types of solid solutions are formed: based on hexagonal modification A-La₂O₃, monoclinic modification B-Dy₂O₃ and cubic modification C-Dy₂O₃ separated by two-phase fields (A+B) and (B+C), respectively. The boundaries of the regions of homogeneity of solid solutions based on A-La₂O₃ are determined by compositions containing 35–40, 20–25, 15–20 mol% Dy₂O₃ at 1500, 1250, 1100 °C, respectively. From the obtained data it follows that the solubility of Dy₂O₃ in the hexagonal modification of lanthanum oxide is 39 mol% at 1500 °C, 23 mol. % at 1250 °C and 16 mol% at 1100 °C. The limits of existence of solid solutions based on monoclinic B-modification are determined by compositions containing 30–35, 65–60 (1250 °С), 35–40, 55–60 (1100 °С) 40–45, 70–75 (1500 °C) mol% Dy₂O₃.In the studied system, with a decrease in temperature from 1500° to 1100°C, there is a decrease in the solubility of La₂O₃ in the crystal lattice of cubic solid solutions of C-type from 16 to 10 mol%.     

Phase diagram of the LaFeO3-LaSrFeO4 system

The phase relationships in the LaFeO₃-LaSrFeO₄ system at temperatures in the range 1000–2100°C in air are investigated, and the phase diagram of the system is constructed. One perovskite-like compound, namely, La₂SrFe₂O₇, which belongs to the Ruddlesden-Popper phases, is revealed in the system.     

Surface Properties of CaO (or BaO)–La2O3–MgO Catalysts and Their Performance in Oxidative Coupling of Methane

CaO–La₂O₃–MgO and BaO–La₂O₃–MgO catalysts with different compositions have been studied for their bulk and surface properties (viz. crystal phases, surface area, acidity/acid strength distribution, basicity/base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) at different processing conditions (reaction temperature, 700–850°C; CH₄/O₂ ratio in feed, 3·0, 4·0 and 8·0 and GHSV, 102000 and 204000 cm³ g⁻¹ h⁻¹). The surface acidity and strong basicity of La₂O₃–MgO are found to be increased due to the addition of a third component (CaO or BaO), depending upon its concentration in the catalyst. The addition of CaO or BaO to La₂O₃–MgO OCM catalyst causes a significant improvement in its performance. Both the CaO- and BaO-containing catalysts show a high activity and selectivity at 800°C, whereas, the activity and selectivity of BaO-containing catalysts at 700°C is lower than that of CaO-containing catalysts. © 1997 SCI.     

Formation peculiarities and optical properties of highly-doped (Y0.86La0.09Yb0.05)2O3 transparent ceramics

Formation peculiarities of highly-doped (Y_0.86La_0.09Yb_0.05)₂O₃ transparent ceramics have been studied by X-ray diffraction and electron microscopy methods. The phase composition evolution of 1.81Y₂O₃∙0.18La₂O₃∙0.01Yb₂O₃ powder mixtures annealed at the temperatures of 1100, 1200, 1300, and 1400 °C has been studied by XRD. It has been shown that Yb₂O₃ phase dissolves in Y₂O₃ matrix in the calcination temperature range of 1300–1400 °C. Complete dissolution of La₂O₃ in Y₂O₃ matrix occurs at temperatures above 1400 °C. La³⁺ ions enter in Y₂O₃ and Yb₂O₃ crystal structures simultaneously in the 1200–1300 °C range, which leads to a remarkable increase in the volume of the corresponding crystal lattices. The possible reasons for suppressing the crystalline growth of Y₂O₃ and Yb₂O₃ cubic phases have been discussed. Finally, (Y_0.86La_0.09Yb_0.05)₂O₃ transparent ceramics have been obtained by solid-state vacuum sintering at 1650–1750 °C. Ceramics synthesized at a temperature of 1750 °C have been characterized by an in-line optical transmittance of 60% and a homogeneous distribution of constituent components within the volume and along the grain boundaries.     

Phase relation studies in the CeO2–La2O3–Er2O3 system at 1500°C

Materials based on CeO₂–La₂O₃–Er₂O₃ system are promising candidates for a wide of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the isothermal section of the phase diagram for 1500 °C was investigated. The phase relations in the CeO₂–La₂O₃–Er₂O₃ ternary system at 1500 °C were studied by X-ray diffraction and scanning electron microscopy in the overall concentration range. To study phase relationships at 1500 °C the as-repared samples were thermally treated in two stages: at 1100 °C (for 300 in air) and then at 1500 °C (for 70 h in air) in the furnaces with heating elements based on Fecral (H23U5T) and Superkanthal (MoSi2), respectively. The solid solutions based on various polymorphous forms of constituent phases and with perovskite-type structure of LaErO₃ (R) with orthorhombic distortions were revealed in the system. No new phases were found. The isothermal section of the phase diagram for the CeO₂–La₂O₃–Er₂O₃ system has been constructed. It was established that in the ternary CeO₂–La₂O₃–Er₂O₃ system there exist fields of solid solutions based on hexagonal (A) modification of La₂O₃, cubic modification of CeO₂ with fluorite-type structure (F), cubic modification Er₂O₃ and with perovskite-type structure of LaErO₃ (R) with orthorhombic distortions. The maximal solubility of ceria in LaErO₃ was found to be around ∼ 2 mol% CeO₂ along the section CeO₂–(50 mol % La₂O₃ –50 mol% Er₂O₃).     

Catalytic Post-Treatment of Automotive Exhaust Gas from Natural Gas Combustion Engines: Potential Interest of Perovskite Materials

This study reports an investigation of the surface properties of Pd-modified perovskite catalysts for NO _x removal from Natural Gas engines. H₂ production from reforming and water-gas-shift reactions can be profitably used for the reduction of NO _x . Particular attention has been paid to the nature of interactions between Pd and LaCoO₃ according to in situ reductive thermal treatments. The catalytic properties have been investigated by temperature-programmed NO desorption and temperature-programmed NO/H₂ reaction. Different experiments performed on partially and extensively reduced catalysts lead to changes in surface reactivity. Interestingly, beneficial interactions with a significant selectivity enhancement to the production of nitrogen is observed on pre-reduced Pd/LaCoO₃ under smooth conditions at 250 °C particularly in the presence of oxygen. More extensive reduction at 450 °C leads to the loss of the structural properties of LaCoO₃ accompanied with partial segregation of CoO _x and La₂O₃. Such structural changes lead to a detrimental effect on the catalytic performances.     

Molten salt synthesis of La2Zr2O7 ultrafine powders

Ultrafine powders of pyrochlore-type La₂Zr₂O₇ were synthesized via a simple molten salt mediated process using zirconium oxide and lanthanum oxide as raw materials, and sodium chloride, potassium chloride and sodium fluoride to form a reaction medium. The effects of reaction temperature, salt/reactant ratio and salt type on the La₂Zr₂O₇ formation were investigated. Among the three attempted salt assemblies (KCl–LiCl, Na₂CO₃–K₂CO₃, and NaCl–KCl–NaF), NaCl–KCl–NaF showed the best accelerating effect on the La₂Zr₂O₇ formation. At a given temperature, the La₂Zr₂O₇ content in the final products increased with the increase in the salt amount. Phase pure submicron sized La₂Zr₂O₇ ultrafine powders were obtained after 3 h firing at 1100 °C with the salt/reactant weight ratio of 5:1 or at 1200 °C with salt/reactant weight ratio of 3:1. The synthesis temperature (1100 °C) was much lower than that required by the conventional solid-state mixing method or a wet chemical method. The “dissolution–precipitation” mechanism had dominated the synthesis process.     

Non-congruence of high-temperature mechanical and structural behaviors of LaCoO3 based perovskites

This paper presents the mechanical behavior of LaCoO₃ and La_0.8Ca_0.2CoO₃ ceramics under four-point bending in which the two cobaltites are subjected to a low stress of ∼8 MPa at temperatures ranging from room temperature to 1000 °C. Unexpected stiffening is observed in pure LaCoO₃ in the 700–900 °C temperature range, leading to a significant increase in the measured Young’s modulus, whereas La_0.8Ca_0.2CoO₃ exhibits softening from 100 °C to 1000 °C, as expected for most materials upon heating. Neutron diffraction, X-ray diffraction and micro-Raman spectroscopy are used to study the crystal structure of the two materials in the RT–1000 °C temperature range. Despite a detailed study, there is no conclusive evidence to explain the stiffening behavior observed in pure LaCoO₃ as opposed to the softening behavior in La_0.8Ca_0.2CoO₃ at high temperatures (above 500 °C).     

Ethanol‐Water‐Derived Sucrose‐Coated‐Al2O3 for Submicrometer AlON Powder Synthesis

Fluffy and homogenous sucrose‐coated‐γ‐Al₂O₃ structured precursor was prepared by drying ethanol‐water sucrose/Al₂O₃ suspension, in which the ethanol content of 85 vol% was optimized. Using the C/Al₂O₃ mixture pyrolyzed from such precursor with 23.2 wt% sucrose, single‐phase AlON powder was synthesized by two‐step carbothermal reduction and nitridation method at 1550°C for 2 h and 1700°C for another 1.5 h. The particle size of the AlON powder was around 0.6–1.0 μm. Compared with those synthesized by the traditional approaches with mechanical C/Al₂O₃, Al/Al₂O₃, or AlN/Al₂O₃ mixtures, the synthesis temperature was reduced about 50°C, and the AlON powder was fine and exhibited good dispersity. Such superiority of this method was attributed to that the pyrolyzed carbon film on Al₂O₃ particle greatly restrained Al₂O₃ coalescence during the thermal treatment.     

Preparation of pure and fully dense lanthanum nickelates Lan+1NinO3n+1 (n = 2, 3, ∞) by post-sintering oxidation process

Lanthanum nickelates with Ruddlesden-Popper structure (La₂NiO₄, La₃Ni₂O₇, and La₄Ni₃O₁₀) and perovskite structure (LaNiO₃) have attracted considerable attention due to their potential applications such as solid oxide fuel cells. Currently, the ionic and electronic conduction properties of La₃Ni₂O₇, La₄Ni₃O₁₀, and LaNiO₃ are not fully understood because it is quite difficult to prepare their dense bodies required for the characterization. The difficulty arises from their narrow thermodynamic stable temperature and oxygen partial pressure ranges. In this study, we successfully obtained dense bodies of single-phase La₃Ni₂O₇, La₄Ni₃O₁₀, and LaNiO₃ via a post-sintering oxidation process. First, dense pellets composed of fine-grain precursors La₂NiO₄ and NiO (~0.5 μm) were prepared by nitrate freeze-drying technique and low-temperature sintering at 1150°C-1225°C. Then they were converted into almost single-phase La₃Ni₂O₇, La₄Ni₃O₁₀, and LaNiO₃ by high-temperature oxidation. La₃Ni₂O₇ and La₄Ni₃O₁₀ were obtained under an oxygen partial pressure of 1 bar at 1275°C and 1200°C-1250°C, respectively, while LaNiO₃ was obtained under of 392 bar at 1250°C using hot isostatic pressing. The relative densities of the pellets exceeded 90%. With regard to their phase stability, decomposition was not detected at 600°C-1100°C in air for at least 100 hour despite their thermodynamic instability.     

Rare earth-first-row transition metal perovskites as catalysts for the autothermal reforming of hydrocarbon fuels to generate hydrogen

Perovskite oxides (ABO₃) containing rare earth elements on the A-site and first-row transition metal elements on the B-site were studied as catalysts for autothermal reforming of liquid hydrocarbon fuels to produce hydrogen for fuel cell systems. Experiments were conducted in a fixed bed microreactor at temperatures of 600–800 °C and gas-hourly space velocities (GHSV) ranging from 4600 to 28,000 h⁻¹ using 2,2,4-trimethylpentane (isooctane) as a surrogate fuel. We have found that the two binary oxides, LaNiO₃ and LaCoO₃, produced high yields of H₂, but were not structurally stable. These perovskites decomposed to La₂O₃ and Ni/NiO or Co/CoO under the reducing conditions present in the reformer. Three other binary oxides, LaCrO₃, LaFeO₃, and LaMnO₃, were structurally stable but significantly less active than LaNiO₃ and LaCoO₃. The partial substitution of chromium, iron, aluminum, gallium, or manganese on the B-site of LaNiO₃ to yield LaB_xNi_1−xO₃ was shown to improve the structural stability without a significant decrease in the H₂ yield. The effects of substituting rare earth elements for La and the substitution of alkaline earth elements on the A-site (La_1−yA_yB_xNi_1−xO₃) on catalyst performance and stability were also investigated. Finally, La_0.8Sr_0.2M_0.9Ni_0.1O₃ catalysts (where M = Cr, Mn, or Fe) were tested with a “benchmark fuel” mixture containing from 0 to 50 ppmw sulfur. These tests showed that using chromium as a stabilizing element in LaNiO₃ imparts the most sulfur tolerance.     

Treatment of exhaust gases from a methanol fueled vehicle over perovskite oxide catalysts

As a study on the treatment of exhaust gases from a methanol-fueled vehicle, catalytic oxidation of formaldehyde and methanol on perovskite-type oxides was performed. La_0.8Sr_0.2MnO₃, La_0.8Sr_0.2CoO₃, YBa₂Cu₃O₇ (superconductor), and ErBa₂Cu₃O₇ (superconductor) were used as catalysts. La-based catalysts were prepared by a citrate method and calcined at 650°C, 800°C, and 900°C, respectively. The catalytic activity of La-based catalysts increased with the increase in the surface area that was dependent on the calcination temperature. Superconductive oxides were also prepared by a citrate method and calcined at 920°C. The catalytic activity of ErBa₂Cu₃O₇ was found to be better than that of YBa₂Cu₃O₇. For La-based perovskite calcined at 650°C, the catalytic activity of La_0.8Sr_0.2MnO₃ was higher than La_0.8Sr_0.2CoO₃. Calcining at 800°C and 900°C, however, the catalytic activity of LLa_0.8Sr_0.2 CoO₃ was higher than La_0.8Sr_0.2MnO₃.     

STRUCTURE OF ISOTHERMAL SECTIONS OF THE DIAGRAM OF THE STATE OF THE SYSTEM ZrO2 – La2O3 – Eu2O3 AT TEMPERATURES 1500 AND 1250 °C

Using the methods of X-ray phase and microstructural analyzes, phase equilibria and structural transformations in the ZrO₂ – La₂O₃ – Eu₂O₃ system at temperatures of 1500 and 1250 ºC in the whole range of concentrations were studied. Based on the obtained data, the corresponding isothermal cross sections are constructed. It is established that the fields of solid solutions are formed in the system on the basis of cubic (F) modification with fluorite type structure, tetragonal (T) modification ZrO₂, monoclinic (B) and cubic (C) modifications Eu₂O₃, hexagonal (A) modification La₂O₃, as well as ordered phases with a structure of the pyrochlor type Ln₂Zr₂O₇ (Py). The boundaries of the phase fields and the parameters of the unit cells of the formed phases are determined. It was found that in the region with a high content of ZrO₂ solid solutions are formed on the basis of tetragonal modification of ZrO₂. The solubility of La₂O₃ in T-ZrO₂is small and is ～ 0.5% (mol.), which is confirmed by X-ray phase analysis and microstructural studies. It is established that at 1500 and 1250°C a continuous series of solid solutions is formed on the basis of an ordered phase of pyrochlor (Py) type Ln₂Zr₂O₇. With decreasing temperature, the region of homogeneity of the specified solid solution narrows. Isothermal cross sections of the state diagram of the ZrO₂-La₂O₃-Eu₂O₃ system at 1500 and 1250°C have a similar structure, although they are characterized by some differences due to the structure of the limiting binary systems. No new phases in the ternary system ZrO₂ – La₂O₃ – Eu₂O₃ were detected at the studied temperatures.     

Phase equilibrium in systems based on oxides of zirconium,lanthanum and samarium

According to the results of the samples studied by X-ray diffraction and microstructural analyzes the phase equilibria in the binary La₂O₃ – Sm₂O₃ and ternary ZrO₂ – La₂O₃ – Sm₂O₃ systems were studied. The boundaries of the phase fields of the binary system are specified and an isothermal cross section of the ternary state diagram of the ZrO₂ – La₂O₃ – Sm₂O₃ system at a temperature of 1500 °C is constructed. No new phases have been identified in the studied systems. It is established that in the ternary system ZrO₂ – La₂O₃ – Sm₂O₃ at 1500 °C fields of solid solutions on the basis of cubic (F) modification with structure of fluorite type, tetragonal (T) modification of ZrO₂, monoclinic (B) modifications of Sm₂O₃, hexagonal (A) are formed. La₂O₃, as well as an ordered phase with a structure of the type of pyrochlore Ln₂Zr₂O₇ (Py). The boundaries of the phase fields and the parameters of the unit cells of the formed phases are determined. A characteristic feature of this isothermal cross section is the formation of a continuous series of solid solutions based on the phase of the pyrochlore type La₂Zr₂O₇ (Sm₂Zr₂O₇). The limiting solubility of Sm₂O₃ in the ordered phase La₂Zr₂O₇ is 16 mol. % along the section Sm₂O₃- (67 mol.% ZrO₂ - 33 mol.% La₂O₃). The solubility of La₂O₃ in the solid solution Sm₂Zr₂O₇ is slightly less and is 11 mol. % along the section La₂O₃- (67 mol.% ZrO₂ - 33 mol.% Sm₂O₃). The isothermal cross-section of the state diagram of the ZrO₂ – La₂O₃ – Sm₂O₃ system at 1500 °C is characterized by the presence of three three-phase (Py + T + F), (A + Py + B), (Py + F + B) and eight two-phase (A + Py), (B + A), (B + Py), (F + B), (T + F), (Py + T), (F + Py-two) areas.