A. V. Osipov

Preparation and thermal transformations of nanocrystals in the LaPO4-LuPO4-H2O system

Powders of nanosized particles of individual and mixed lanthanum and lutetium orthophosphates are synthesized. The grain growth process is studied in the temperature range of 200–1100°C. Temperature and concentration regions of existence of the solid solutions based on hexagonal and monoclinic forms of LaPO4 as well as on tetragonal LuPO4 are determined.

Synthesis, mutual solubility, and thermal behavior of nanocrystals in the LaPO4-YPO4-H2O system

Nanopowders of lanthanum and yttrium orthophosphates have been synthesized. The growth of nanocrystals has been investigated in the temperature range 200–1100°C. The temperature-concentration limits of the existence of the solid solutions have been determined. The thermal behavior of the orthophosphates has been studied over the entire range of lanthanum and yttrium concentrations.

Crystallization and thermal transformations in nanocrystals of the YPO4-LuPO4-H2O system

Nanocrystals of yttrium lutetium phosphates of the general formula Y1−xLuxPO4 · nH2O are synthesized. The temperature dependence of the nanocrystal size is investigated in the range 200–1100°C. The formation of a series of continuous solid solutions belonging to the tetragonal crystal system is revealed, and the limits of their thermal stability are determined.

The influence of the particularities of synthesis on the physicochemical properties of nanosized powders and ceramic samples of REE orthophosphates

Sol–gel synthesis of La1–xYxPO4 · nH2O orthophosphates has been conducted via a method of reverse precipitation, and the obtained powders have been studied with X-ray phase analysis and simulteneous thermal analysis, including differential scanning calorimetry and thermogravimetry (DSC/TG). For the ceramic samples obtained from the powder, the microhardness has been determined depending on the temperature of the heat treatment. The thermal behavior of the samples has been studied via the method of dilatometry.

Synthesis of nanopowders and physicochemical properties of ceramic matrices of the LaPO 4 –YPO 4 –(H 2 O) and LaPO 4 –HoPO 4 –(H 2 O) systems

Sol-gel method was used to synthesize nanosize powders in the LaPO4–YPO4–(H2O) and LaPO4–HoPO4–(H2O) systems. Dense ceramic samples with high microhardness (up to 25 GPa) were formed from these powders by sintering at temperatures of up to 1600°C. The isomorphic capacity of the monoclinic LaPO4 matrix for the second component (yttrium or holmium) simulating radioactive nuclides of the actinide-rare-earth fraction was found to be high. The composites are stable in aqueous solutions, which is indicated by the low concentration of lanthanum and yttrium ions during leaching test (~10–7 g L–1). The results obtained in the study can be used to develop new high-efficiency ceramic matrices for solidification of the actinide-rare-earth fraction of liquid wastes formed in processing of the spent nuclear fuel.

Chemical and thermal stability of phosphate ceramic matrices

Nanosized powders of orthophosphates in the LaPO4–YPO4–H2O system have been synthesized by the sol–gel method using the reverse precipitation. The obtained powders served as a base to produce compact ceramic matrices. The matrices’ microhardness has been determined and the dependence of microhardness on the sintering temperature and duration has been established. The dilatometry method was used to study the thermal behavior of ceramic matrix samples and to estimate their thermal expansion coefficient. The stability of La1–xYxPO4 ceramic matrices to leaching in distilled water at room temperature has been determined.

Nanopowders of orthophosphate LaPO4-YPO4-H2O system and ceramics based on them

Nanopowders of orthophosphate LaPO4-YPO4-H2O system have been synthesized via the solgel method, and the limits of the mutual solubility of components have been specified through the calculation of the parameters of the unit cell. The dense ceramics were prepared based on the La1 − xYxPO4 · nH2O nan-opowders at 1000 and 1200°C. The porosity, microhardness, and bending strength of the ceramics were determined, and the dependence of the microhardness on the calcination time was established. The thermal behavior of the samples was studied by dilatometric method and the thermal coefficient of linear expansion of the ceramics was estimated.

Physical–chemical properties of nanopowders and ceramic samples of REE orthophosphates

A series of physical–chemical studies of a series of binary REE orthophosphate systems has been performed: LaPO4–DyPO4–H2O, LaPO4–YPO4–H2O, LaPO4–LuPO4–H2O, YPO4–LuPO4–H2O, and YPO4–ScPO4–H2O. Nanopowders of Ln1 −xLnx PO4 · nH2O orthophosphates have been synthesized by the sol–gel method using direct and reverse precipitation techniques. Ceramic samples were produced from the nanopowders, and their physical–mechanical properties were determined depending on the thermal treatment temperature and duration. The ceramic samples’ thermal behavior has been investigated by the dilatometry method. The results have been compared depending on the technique of nanopowder synthesis.

Structure and superconducting properties of layered perovskite-like compounds Y1 − 2xCaxPrxBa2Cu3Oy and Y1 − xBa2PrxCu3 − xZnxOy

The conditions of preparation of Y1 − xPrxBa2Cu3 − xZnxOy and Y1 − 2xCaxPrxBa2Cu3Oy solid solutions with an Y-123-type structure in the orthorhombic crystal system by the method of solid-phase chemical reactions have been determined. The concentration dependences of the unit cell parameters for these solid solutions have been established. The temperature dependences of the resistivity of the synthesized compounds have been investigated, the critical temperatures of the superconducting transition have been determined, and their variation as a function of the type and content of the introduced dopants has been analyzed. It has been demonstrated that, in the Y1 − xPrxBa2Cu3 − xZnxOy samples, individual dopants have a combined effect on the suppression of the superconducting properties, whereas in the Y1 − 2xCaxPrxBa2Cu3Oy samples, calcium and praseodymium ions interact with each other when they are simultaneously introduced into the yttrium sublattice.