Theoretical explanation for Raman and ESR spectra of V3+ ions in salt guanidinium vanadium sulfate hexahydrate

The Raman spectra and electronic spin resonance (ESR) parameters (spin-Hamiltonian parameter g factors, zero-field splitting parameter D, and hyperfine structure constant A) for the trigonal V³⁺ centers in salt guanidinium vanadium sulfate hexahydrate (GVSH) are calculated from the complete diagonalization (of energy matrix) method. The theoretical results are in agreement with the experimental findings and the trigonal crystal-field parameters are determined. The difficulty in explaining ESR parameters of V³⁺ in GVSH is removed.     

Study of ferroelectric nanodomains and the effect of grain size in BaTiO3 ceramics

Nanodomains and grain-size effects in BaTiO₃ have been studied theoretically. In this article, we have calculated the long-range Coulomb interaction between ferroelectric nanodomains in a single BaTiO₃ grain, and obtained information on the domain structure at various temperatures and grain sizes. The relation between transition temperature and the grain size is obtained by incorporating the domain-wall energy, the surface energy, and the stress energy into the Landau–Ginzburg free-energy density. The results show that 180° domains exist in ferroelectric BaTiO₃ nanoceramics. At room temperature, with the decreasing grain size, the domain width does not decrease monotonically; when the grain size reduces to 18?nm, the grain becomes a single domain, and when less than 12?nm, the ferroelectric phase disappears. With the decreasing grain size the temperature of the cubic-tetragonal phase transition is reduced, while the temperatures of the tetragonal–orthorhombic and orthorhombic–rhombohedral phase transitions reach a maximum when the grain sizes are in the vicinity of 200?nm. The theoretical results are compared with experimental data.     

Investigations of the optical spectra and EPR g-factors for the tetragonal Ce3+ centers in YPO4 and LuPO4 crystals

The optical spectral band positions and EPR g-factors (g_‖ , g _⊥) for the tetragonal Ce³⁺ centers in YPO₄ and LuPO₄ crystals with the zircon-structure are calculated using a complete diagonalization (of the energy matrix) method (CDM) related to 4f¹ ions in tetragonal symmetry. In this method, the Zeeman interaction term are added to the Hamiltonian in the conventional CDM and so no perturbation calculations are required to obtain the g factors. The crystal-field parameters used in the calculations are obtained from the superposition model in which the local lattice relaxation related to the bonding lengths is considered. The calculated results are in reasonable agreement with the experimental values. It is found that the four observed optical bands for both the systems can be attributed to Ce³⁺ ions in a tetragonal crystal field.