Djuniadi Arifin Sagala

Lattice Energy Calculations for Ordered and Disordered Ba(Zn1/3Ta2/3)O3

Lattice energies were calculated for ordered and disordered Ba( Zn 1/3 Ta 2/3 ) O 3 . Lattice summations were carried out for both long-range electrostatic and short-range Born-Mayer type interaction energies by using the rigid ion model. Electronic polarizations were taken into account to calculate the energy contribution from deformable charges of oxygen and barium ions as a strong local field exists in the ordered structure. The interaction energy and the internal energy of dipole moments induced by local field were determined. It was shown that the lattice energy of the ordered structure is 2.15 eV lower than that of the disordered structure. This result is consistent with the reported experimental results which demonstrated the stability of the ordered structure for Ba( Zn 1/3 Ta 2/3 ) O 3 .

Spinodal decomposition in tetragonal TiO2‐SnO2 system

A microscopic calculation was carried out for spinodal decomposition in the tetragonal TiO2‐SnO2 system by taking the contribution of the elastic free energy into account. Necessary elastic constants for the solid solutions and the elastic free energy of modulated structure were calculated in terms of interatomic potentials. Theoretical study and computer simulation were carried out for the dynamics of spinodal decomposition on the basis of a nonlinear diffusion equation derived from a coarse grained free energy. The time evolution of the microstructure and the effect of elastic strain on the decomposition process were investigated by Langer’s approximate method and the finite difference method. It was shown that the composition fluctuation along the [001] direction develops in the first stage, the formation of interface and the grain‐growth appear in the second stage, and the interface dislocations are introduced in the third stage. These results agree with the experimental observations in the tetragonal...