The development of new materials for various fields of science and technology has always been an important and priority task for scientists around the world. Recently, more and more interest in the creation of new materials has been drawn to compounds based on the perovskite phase with the general formula ABO 3 . The ability of the perovskite structure to adapt to different combinations of chemical elements leads to the possibility of creating new materials with different physical and chemical characteristics. In the present study, an ordered phase with a LaLuO 3 perovskite-type structure was synthesized using the mechanosynthesis technique. The obtained material was sintered by spark plasma sintering. It was found that the formation of an ordered phase with a perovskite-type structure occurs directly during spark plasma sintering. A dense (99.7%) single-phase sample with a LaLuO 3 perovskite-type structure was obtained. Despite the rather high density of the obtained sample (99.7%), it remains translucent for a number of reasons: the obtained sample is characterized by randomly oriented grains, which creates additional optical scattering.

The phase equilibria in the ternary CeO2-La2O3-Ho2O3 and binary La2O3-Ho2O3 and CeO2-Ho2O3 systems at a temperature of 1500 degrees C in the whole concentration range were studied. No new phases have been identified in these systems. An isothermal cross section of the state diagram of the CeO2-LaO2-Ho2O3 system at a temperature of 1500 degrees C is constructed. It was found that the following solid solutions are formed in the studied systems: cubic solid solutions with a structure of fluorite type F-CeO2, as well as solid solutions based on monoclinic (B), hexagonal (A) and cubic (C) modifications of Ln2O3. It was found that cubic solid solutions of the fluorite type FCeO2 are in equilibrium with all phases formed in the ternary system CeO2- La2O3-Ho2O3 at a temperature of 1500 degrees C. The boundaries of phase fields and lattice parameters of the formed phases for all investigated systems are determined. A brief description of the structure of isothermal cross sections of ternary state diagrams of systems of the CeO2-La2O3-Ln2O3 series at a temperature of 1500 degrees C is given. It is established that the systems of this series have a similar structure, although they are characterized by some differences due to the polymorphism of the original components.

By the arc-melting method, we obtain a high-entropy boride by adding boron powder to the Ti 30 Zr 25 Hf 15 Nb 20 Ta 10 alloy. The data of X-ray phase diffraction analysis show that the Ti 30 Zr 25 Hf 15 Nb 20 Ta 10 alloy is a single-phase alloy with body-centered cubic (bcc) structure and that the main phase of the Ti 15.8 Zr 13.4 Hf 7.8 Nb 10.5 Ta 5.3 B 47.2 alloy is MeB boride with insignificant amount of bcc and hexagonal close-packed structures. The microstructure of the obtained alloys is analyzed and it is shown that the addition of boron leads to the segregation of constituent components of the alloy. The addition of boron also increases the level of hardness from 3.5 to 33.5 GPa, the modulus of elasticity from 75 to 290 GPa, and the yield strength from 1.06 to 10.28%.

The evolution of phase composition and thermal oxidation behavior of high-entropy AlCrFeCoNiMn x alloys ( x = 0.5 and 1) during long-term oxidation at 900°C were studied. A single- phase ordered (B2) bcc alloy formed in the starting as-cast state regardless of manganese content. The scale phase composition varied with exposure time and manganese content. After 10 h of oxidation, high-entropy spinel-type MeMn 2 O 4 , as well as Mn 3 O 4 and Al 2 O 3 , formed on the AlCrFeCoNiMn alloy, while only Mn 3 O 4 and Al 2 O 3 oxides emerged on the AlCrFeCoNiMn 0.5 alloy. Increase in the oxidation time for the equiatomic alloy up to 25 h led to spinel NiMn 2 O 4 and bixbyite FeMnO 3 in the oxide scale; Mn 3 O 4 and Al 2 O 3 were also present. The phase composition of the oxidized layer on the AlCrFeCoNiMn 0.5 alloy did not change. After 50 h, the structure of the oxide scale was similar for both alloys and consisted of NiMn 2 O 4 , FeMnO 3 , Mn 3 O 4 , and Al 2 O 3 in different ratios. The oxidation kinetics of the alloys naturally depended on the manganese content: the higher the manganese content, the higher the oxidation rate. A continuous layer of the fcc solid solution rich in chromium, iron, and cobalt was observed under the scale in both alloys. An internal oxidation area was also found in the subscale layer of the AlCrFeCoNiMn alloy. Long-term (more than 50 h) oxidation at 900°C substantially changed the phase composition of the alloy matrices: the bcc (B2) solid solution underwent spinodal decomposition to form bcc and fcc phases and tetragonal σ phase. Analyses of the alloy matrices showed a sharp increase in their microhardness after annealing. This can be attributed to the formation of a significant amount of the σ phase.

The phase equilibria in the ZrO2–HfO2–Nd2O3 ternary system at 1500 °C and 1700 °C were studied over the whole concentration range by X-ray diffraction and microstructural analyses. Corresponding isothermal sections were constructed from the data obtained. It was found that solid solutions in this system are derived from a tetragonal (T) modification of ZrO2, a monoclinic (M) modification of HfO2, a hexagonal (A) modification of Nd2O3, a cubic phase with a fluorite (F) structure of ZrO2 (HfO2), and an ordered phase with a pyrochlore (Py) structure of Nd2Zr2O7 (Nd2Hf2O7). The phase boundaries and unit cell lattice parameters were determined. The solubility of Nd2O3 in M − HfO2 is pretty low and about less than 1 mol%, as confirmed by XRD and microstructural analyses. The ordered pyrochlore-type (Py) phase of Nd2Zr2O7 (Nd2Hf2O7) forms continuous series of solid solutions at 1500 °C and 1700 °C. The homogeneous region of these continuous series of solid solutions changes insignificantly with increasing temperature. The changes in the construction of the isothermal section of the ZrO2-HfO2-Nd2O3 phase diagram at 1500 °C compared to 1700 °C are associated with the thermal stability of cubic fluorite-type (F) solid solutions. Other phases in the ZrO2-HfO2-Nd2O3 ternary system are not detected at the studied temperatures.

Phase equilibria and structural transformations in the La2O3–Y2O3–Gd2O3 system at 1600°C were studied by X-ray diffraction, electron microscopy, and petrography in the entire composition range. Fields of solid solutions based on hexagonal (A) modification of La2O3, cubic (C) modification of Y2O3, and monoclinic (B) modification of La2O3 (Gd2O3) were identified in the system. The starting materials were La2O3, Gd2O3, and Y2O3 (99.99

In the presented work, based on the results obtained by X-ray diffraction and microstructural analysis, phase equilibria have been studied and an isothermal section of the ZrO2–HfO2–Nd2O3 ternary phase diagram at 1100 °C has been constructed. Unit cell parameters were calculated by the least squares method using the LATTIC software. The International Powder Standards Committee database (JSPSDS International Center for Diffraction Data 1999) was used to determine the phase composition.It was found that in the studied system are formed regions of solid solutions based on a cubic fluorite-type (F) modification, a tetragonal (T) modification of ZrO2, a monoclinic (М) modification of HfO2, a hexagonal (А) modification of Nd2O3, as well as an ordered (Py) pyrochlore phase of Nd2Zr2O7 (Nd2Hf2O7). The boundaries of the phase regions and the unit cell parameters are determined. A continuous series of solid solutions based on the ordered pyrochlore (Py) phase of Nd2Zr2O7 (Nd2Hf2O7) at the studied temperature is derived. The unit cell parameters of the ordered pyrochlore (Py) phase vary from a = 1.0633 nm for the two-phase composition (Py + M), 47.5 mol% ZrO2 – 47.5 mol% HfO2 – 5 mol% Nd2O3) to a = 1.0639 nm for the boundary composition of the solid solution (37.5 mol% ZrO2 – 37.5 mol% HfO2 – 30 mol% Nd2O3) and then up to a = 1.0648 nm for the two-phase (Py + A) composition (30 mol% ZrO2 – 30 mol% HfO2 – 40 mol% Nd2O3) which located along the Nd2O3 – (45 mol% ZrO2 – 55 mol% HfO2) constant ratio line. The studied isothermal section is characterized by the formation of two three-phase (Py + F + M and F + T + M) and six two-phase (A + Py, Py + M, Py + F, F + M, T + M, F + T) regions. In the ZrO2–HfO2–Nd2O3 ternary system, no new phases are detected at the temperatures studied.

The phase equilibria in the ternary La 2 O 3 -Y 2 O 3 -Gd 2 O 3 system at 1500 °C were studied by X-ray di ff raction, petrography and electron microscopy in the overall concentration range. The samples of di ff erent 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 constituent phases and ordered phase of LaYO 3 were revealed in the system. The isothermal section of the phase diagram for the La 2 O 3 -Y 2 O 3 -Gd 2 O 3 system has been developed. It was established that in the ternary La 2 O 3 -Y 2 O 3 -Gd 2 O 3 system fields of solid solutions exist based on hexagonal (A) La 2 O 3 phase, monoclinic (B) modifications of La 2 O 3 and Gd 2 O 3 , cubic (C) modification of Y 2 O 3 , as well as perovskite-type structure of LaYO 3 (R) with rhombic distortions. The systematic study that covered the whole compositional range excluded the formation of new phases. The refined lattice parameters of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.

The phase equilibria in the ternary system ZrO2-HfO2-Sm2O3 were studied by X-ray diffraction and microstructural analyses. The formation of new phases in the Zr & Ocy;2-HfO2-Sm2O3 system at 1500 degrees & Scy; was not observed. It is established that in the studied system at 1500 degrees C the fields of solid solutions based on tetragonal (T) modification of Zr & Ocy;2, monoclinic (M) modifications of HfO2, and monoclinic (B) modifications of Sm2O3, and ordered phase with the structure of pyrochlore-type (Py) Ln2Zr2O7 (Ln2Hf2O7) are present. The boundaries of the phase fields and the parameters of the unit cells of the formed phases are determined. The studied isothermal cross section of the Zr & Ocy;2-HfO2-Sm2O3 system is characterized by the formation of continuous series of cubic solid solutions based on a phase with a structure of the pyrochlore-type Sm2Zr2O7 (Sm2Hf2O7) and a structure of the fluorite type F-ZrO2 (HfO2). It is established that two regions of homogeneity of cubic solid solutions are formed in the determined system. The existence of these regions of homogeneity is due to the rupture of the solubility of the F-ZrO2 (HfO2) phase in the region of the existence of an ordered phase with a pyrochlore-type structure Sm2Zr2O7 (Sm2Hf2O7). It is established that the solid solution based on a cubic modification with fluorite-type structure exists in equilibrium with all phases observed in the system. Isothermal section of the phase diagram of the system ZrO2-HfO2-Sm2O3 at 1500 degrees C has been characterized by the presence of one three-phase (F + T + M), as well as five two-phase (B + F, two-F + Py, M + F, T + F) regions.

We study the influence of electron concentration, lattice distortion, and phase ratio on the hardness, elasticity modulus, and normalized hardness of high-entropy two-phase alloys. It is shown that the fractions of phases depend on the concentrations of electrons. A sharp increase in the FCC phase is observed for electronic concentrations higher than 8 el/at. For high-entropy two-phase alloys, we establish a linear dependence of the normalized hardness on the dimensional mismatch. The values of normalized hardness increase from 0.025 to 0.043 as the level of distortion increases from 2.3 to 4.3%.

The Cu–Ti–Zr system and associated multicomponent systems are of practical interest as their alloys show high bulk glass forming ability. The Cu–Ti–Zr system is divided into two independent subsystems (Ti–CuTi2–CuZr2–Zr and Cu–CuTi2–CuZr) by the quasibinary vertical CuTi2–CuZr2 section. In this paper, phase equilibria in the Ti–CuTi2–CuZr2–Zr subsystem were experimentally studied. The structure of the as-cast binary and ternary alloys and the temperature of phase transformations in the samples that were cast and annealed at 750°C were studied by physicochemical analysis methods. The results were used to construct the liquidus and solidus surfaces, phase diagram, and vertical sections with 10, 20, and 30 at.% Cu, confirm the congruent formation of binary CuTi2 and CuZr2 compounds at 1012 and 1000°C, and find the composition and temperature of invariant eutectic reactions with their participation. The liquidus surface consists of two primary crystallization surfaces of infinite series of (βTi, βZr) (β) and Cu (Ti, Zr)2 (γ) phases, which intersect along the univariant eutectic curve. The liquidus temperatures decrease from the boundary binary systems to the ternary one, reaching the minimum at 845 °C. The solidus surface is characterized by the coexistence of the β and γ phases (β + γ range) over the entire composition range. The copper solubility is from 5 to 8 at.% in the β phase and up to 2 at.% in the γ phase. This two-phase region is formed through the eutectic L ⇄ (βTi, βZr) + Cu (Ti, Zr)2 reaction. There is also a minimum at 845°C on the solidus surface. The compositions of the two solid and one liquid phases coexisting at the minimum temperature are found on a single tie-line, along which the three-phase equilibrium is invariant. The compositions of the phases in this equilibrium are as follows: Lmin—Cu30Ti37Zr33, βmin—Cu10.5Ti62Zr28.5, and γmin—Cu32Ti35Zr33 (at.%). According to differential thermal analysis, the minimum temperature of the eutectoid (βTi, βZr) ⇄ (αTi, αZr) + Cu(Ti,Zr)2 transformation is 570°C.

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 ? 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 CeO(2)with structure of fluorite type, monoclinic (B), cubic (C) and hexagonal (A) modifications of Ln(2)O(3). In the La2O3-Dy2O3 binary system (1500-1100 C) three types of solid solutions are formed: based on hex-agonal 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 modifi-cation 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 C), 35-40, 55-60 (1100 C) 40-45, 70-75 (1500 C) mol% Dy2O3 . In the studied system, with a decrease in temperature from 1500 to 1100C, there is a decrease in the sol-ubility of La(2)O(3)in the crystal lattice of cubic solid solutions of C-type from 16 to 10 mol%.

Phase equilibria in the La 2 O 3 –Lu 2 O 3 –Yb 2 O 3 system were studied by X-ray diffraction and electron microscopy for the first time at 1600°C over the entire composition range. Solid solutions based on various crystalline modifications of the starting components and ordered perovskite-type phases were found to form in the system. The starting materials were La 2 O 3 , Lu 2 O 3 , and Yb 2 O 3 (99.99%). The samples were prepared with a concentration step of 1–5 mol.%. Weighed oxides were dissolved in HNO 3 (1 : 1) and then the solutions were evaporated and decomposed at 800°C for 2 h. The samples were heat treated in three stages: at 1100°C (for 163 h), at 1500°C (for 70 h), and at 1600°C (for 10 h) in air. The samples were subjected to X-ray powder diffraction employing a DRON-3 diffractometer at room temperature (Cu-K α radiation, Ni filter). The scan angle was 0.05–0.1° in the range 2θ = 15–90°. The isothermal section of the La 2 O 3 –Lu 2 O 3 –Yb 2 O 3 phase diagram at 1600°C shows three single-phase (A-La 2 O 3 , R, C-Lu 2 O 3 (Yb 2 O 3 )) and two two-phase (C + R, A + R) regions. The system forms continuous areas of solid solutions based on the cubic modification of C-Lu 2 O 3 (Yb 2 O 3 ) and the ordered perovskite-type phase (R phase). The solubility limits were determined and composition dependences for lattice parameters of the phases formed in the system were plotted. The boundary solubility of lutetium oxide in the R phase is 5 mol.% in the Lu 2 O 3 –(50 mol.% La 2 O 3 –50 mol.% Yb 2 O 3 ) section. The homogeneity range of the C-Lu 2 O 3 solid solutions extends from 93 to 100 mol.% Lu 2 O 3 in the Lu 2 O 3 –(50 mol.% La 2 O 3 –50 mol.% Yb 2 O 3 ) section. The solid solutions form through isovalent substitution, and the stability of ordered phases and solid solutions is determined by the shape factor of lanthanides.

Phase equilibria during solidification in the Al-Cr-Co system in the range of compositions 0-70 at.% Al were studied using optical microscopy, scanning electron microscopy, electron probe microanalysis, differential thermal analysis and x-ray diffraction. Solidus and liquidus surfaces, a melting diagram as their superposition, a Scheil diagram for solidification, as well as series of isopleths were constructed for the first time. Solid solutions based on Cr, αCo, Cr5Al8 (γ3 and γ1 phases), CoAl, Co2Al5 binary compounds and the ternary compound τ5 take part in phase equilibria. The monoclinic ternary compound τ5 forms by peritectic reaction L + γ1 + Co2Al5 ↔ τ5 at 1065 °C. Four invariant four–phase reactions and one invariant three–phase reaction involving liquid take place at 1280, 1175, 1110, 1065 and about 1480 °C, respectively. Isopleths 10, 20, 30 and 40 at.% Al as well as 40 at.% Cr demonstrate peculiarities of the phase diagram.

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.

X-ray diffraction revealed that the ZrNi1.2Mn0.5Cr0.2V0.1 alloy powder exposed to air showed quantitative surface phase composition of varying stability depending on the weight of samples. When a powder sample with a lower weight (5 g) was exposed to air for two days, its quantitative phase composition was quite stable and varied within 1%, while a powder sample with a greater weight (40 g) had polymorphic C15 and C14 phases (amount of the C15 phase became 4% higher and that of the C14 phase became 4% lower). The sample that was more stable in exposure to air for two days demonstrated a greater cyclic life in the hydrogeneration–dehydrogenation process. The quantitative phase composition of the lighter sample exposed to air was assumed to be also stable in the hydrogenation–dehydrogenation process and to promote a greater cyclic life, while changes in the quantitative phase composition affected the cyclic life. The activation of electrodes compacted from freshly made ZrNi1.2Mn0.5Cr0.2V0.1 alloy powders depended on the type of nickel and manganese used for melting and occurred at different rates. In the case of electrolytic nickel and electrolytic manganese in alloy melting (40 g samples), the maximum discharge capacity was reached six cycles sooner than in the case of cathode nickel and ferromanganese. Contrastingly to the activation rate, the cyclic life of electrodes made of the ZrNi1.2Mn0.5Cr0.2V0.1 alloy powders using different types of nickel and manganese primarily depended on the weight of the samples. The cyclic life curves for the electrodes pressed from freshly ground powders from the 5 g alloy samples (cathode nickel and ferromanganese in one sample and cathode nickel and electrolytic manganese in the other sample) matched. The cyclic life curves for the electrodes made of the 40 g samples (cathode nickel and ferromanganese in one sample and electrolytic nickel and electrolytic manganese in the other sample) matched as well. The best cyclic life was demonstrated by the electrodes made of the lighter powder samples. This was likely to be associated not only with the sample sizes but also with the use of cathode nickel in alloy melting. The loss of discharge capacity by these electrodes for 80 cycles was 8%, while that for the electrodes made of the powders ground from the heavier samples was 50%.

A process was developed for the production of agglomerated carbonyl nickel powders with spherical particles ranging from 45 to 71 μm. The powders are intended to make spongy oxide/nickel cathodes. The idea relied on the separation of integral and local compaction effects in the sintering of agglomerated powders. The morphology and particle size of the powders were examined by scanning electron microscopy using a Superprobe-733 analyzer. The nickel powders were chemically tested to determine their carbon content with automatic coulometric titration by pH values employing an AN-7529U rapid analyzer. The agglomerated carbonyl nickel powders with spherical 45–71 μm particles were produced from PNK-1L5 carbonyl nickel powders with average particle sizes of 4 μm by annealing without mechanical grinding. The optimum process of producing nickel powders with 45–71 μm particles involves stage-by-stage annealing of agglomerated particles at 400, 500, and 600°C for 0.5 h with intermediate sifting through sieves 071 and 045. Testing of the spongy oxide/nickel cathodes produced in compliance with the agglomeration process for the fine PNK-1L5 nickel powders showed that they could be used to replace the PNK-2K10 nickel powders.

The evolution of phase composition and mechanical properties and the formation of oxide layers on Fe 40–x NiCoCrAl x (x = 5 and 10 at.%) alloys in long-term oxidation at 900 and 1000°C were studied. In the initial cast state, depending on the aluminum content and valence electron concentration, the alloys contain only an fcc solid solution (VEC = 8 e/a) or a mixture of fcc and bcc phases (VEC = = 7.75 e/a). Thin continuous oxide scales containing Cr 2 O 3 and NiCr 2 O 4 spinel formed on the surface of both alloys oxidized at 900°C for 50 h. A further increase in the annealing time to 100 h leads to the formation of aluminum oxide Al 2 O 3 in the scale on the Fe 30 Ni 25 Co 15 Cr 20 Al 10 alloy, having high protective properties. An increase in the oxidation temperature to 1000°C results in partial failure of the protective layer on the alloy with 10 at.% Al. Long-term holding at 900°C (100 h) + 1000°C (50 h) does not change the phase composition of the Fe 35 Ni 25 Co 15 Cr 20 Al 5 alloy matrix, being indicative of its high thermal stability. In the two-phase Fe 30 Ni 25 Co 15 Cr 20 Al 10 alloy, the quantitative ratio of solid solutions sharply changes: the amount of the bcc phase increases from 4 to 54 wt.% and its B2-type ordering is observed. The mechanical characteristics of the starting alloys and those after long-term high-temperature annealing were determined by automated indentation. The hardness (H IT ) and elastic modulus (E) of the cast Fe 35 Ni 25 Co 15 Cr 20 Al 5 alloy are equal to 2 and 147 GPa, respectively, and decrease to 1.8 and 106 GPa after a series of long-term annealing operations. The Fe 30 Ni 25 Co 15 Cr 20 Al 10 alloy shows the opposite dependence: H IT increases from 2.5 in the initial state to 3.1 GPa after annealing and E decreases from 152 to 134 GPa. This indicates that the Fe 30 Ni 25 Co 15 Cr 20 Al 10 alloy is promising as a high-temperature oxidation-resistant and creep-resistant material.

Phase equilibria and structural transformations in the binary La2O3–Er2O3 system at 1100–1500°C have been studied by X-ray diffraction, microstructural analysis, and electron microprobe analysis over the entire composition range. Solid solutions based on the hexagonal modification of A-La2O3, cubic modification of C-Er2O3, and ordered perovskite-type LaErO3 (R) phase with orthorhombic distortion have been established to exist in the system. The boundaries of phase regions and lattice parameters of the phases formed in the system have been determined. The ordered perovskite-type LaErO3 (R) phase is present in the composition range 45–51 mol.% Er2O3 at 1100 and 1500°C. When temperature decreases to 1100°C, the homogeneity ranges of the C-Er2O3 and A-La2O3 solid solutions are reduced. The complete La2O3–Er2O3 phase diagram has been constructed over the composition range 800–2400°C using literature data.