ИСТИНА

The complex oxides and phosphates of 3d-elements, having nonstoichiometric composition, attracted increasing interest in modern technology. Oxides are known as superconductors, cathode materials for fuel cell, catalysts; phosphates find the application as cathode materials for rechargeable batteries. A wide variation of composition followed by changing of oxidation state of 3d-elements, formation of cation and anion vacancies are taking place under material's performing and functioning. The problems of estimation of the thermodynamic stability these materials on the base of thermochemical data, followed by modelling of crystal lattice energy, are in focus in this work. The main objects under consideration are complex cuprates La2-xSrxCuO4-δ and phosphates of 3d-elements AMPO4 (A = NH4, Li; M = Mn, Fe, Co, Ni), having layered crystal structure. The La2-xSrxCuO4-δ structure represented a sequence of perovskite type copper-oxide and rock salt {La2-xSrxO2} layers. The interatomic distances in copper-oxide layers are accommodated to ion pack of atoms in La2-xSrxO2 layers by means of variation of copper oxidation state and formation of oxygen vacancies. In layered phosphates 3d-elements have to accommodate within oxygen atoms of tetrahedral phosphate anions. The lattice energy was modeled as a function of composition and copper oxidation state using experimental data on crystal structure and enthalpies of formation. Entropy values were taken from the reference data or calculated from the experimental data on temperature dependence of the specific heat. The dependences of the lattice energy La2-xSrxCuO4-δ from x(Sr) and copper oxidation state were plotted. It was shown that the main contribution to the change of lattice energy makes copper-oxygen layers at changing the copper oxidation state and formation of oxygen vacancies. The oxidation of copper increases the stability of crystal lattice, but removing of oxygen, followed by oxygen vacancies formation, reduces stability. The replacing 3d-elements in phosphate matrix decreases the enthalpy of formation in Mn - Co row, despite the decrease of the ionic radius of the element and reducing of lattice parameters.