The structure and elastic properties of MgSiO3, a major mantle-forming phase, have been simulated using computer models which predict the minimum energy structure by using interatomic pair potentials to describe the net forces acting between the atoms. Four such interatomic potentials were developed in this study, and are compared with potential N1 of Miyamoto and Takeda (1984). The most successful potential (W3) was derived by fitting the short range potential parameters to both the experimentally obtained structural and elastic properties of MgSiO3 perovskite. The relative stabilities of some of the possible perovskite polymorphs, the orthorhombic, cubic, and tetragonal phases and hexagonal polytypes, were evaluated at 0 K and between 1 bar and 2 Mbar. The orthorhombic phase is found to be stable at all but the highest pressures, where the cubic phase may be stable. The temperature of the ortho-rhombic to cubic transition may decrease with increasing pressure. The energy of a stacking fault on (110) in the cubic phase was estimated using the ANNNI model and found to be about 1.95 J m−2 using potential W3. The distance of separation of partial dislocations of this type is predicted to increase with increasing pressure from 8.4 Å at 1 bar to 9.2 Å at 1 Mbar.

PLZT of the compositions 0≤L≤12, and 0≤T≤10 was studied in order to describe the structure of the phases as a function of composition. This range contains a mixed region with PLZT+La2Zr2O7, an orthorhombic, a rhombohedral (hexagonal) phase, a tetragonal phase, and a mixture of different PLZT phases. Each phase pure composition is described by X-ray diffraction.

The change in the orthorhombic structure of PbZrO3 was studied as a function of the La substitution for Pb and Ti substitution for Zr. Two types of changes can occur: (1) a change in the atom coordinates toward the positions for a perfect cubic perovskite lattice; and (2) a change of orthorhombic unit cell parameters so that ao, bo, and co exactly fit with the cubic cell parameter ac. Therefore, ao=ac√2, bo=ac.2√2, and co=ac.2, where ao, bo, and co are the orthorhombic cell parameters, and ac is the cubic cell parameter. Substitution of Pb by La in the orthorhombic PLZT leads to both a change in atom coordinates and a change in unit cell parameters toward the perfect cubic structure, especially for La≥4. Substitution of Zr by Ti in the orthorhombic PLZT leads to similar atom coordinate changes, but the unit cell parameters do not change. The composition 0/92.5/7.5 contains a major tetragonal phase and a minor orthorhombic phase. There are only small differences in the orthorhombic structure between the A and the B composition of PLZT. The A composition has a structure closer to the cubic structure than the B composition.

Powder X-ray diffraction (XRD) data were collected for Pr0.7Ba0.3MnO3. This sample was prepared using the conventional solid state reaction by mixing Pr6O11, Mn2O3, and BaCO3 up to 99.9% purity at 1400 °C in air for 60 h. XRD analysis using the Rietveld method was carried out and it was found that this manganite sample has orthorhombic symmetry with Pnma space group. The lattice parameters are found to be a=5.4900 Å, b=7.7578 Å, and c=5.5227 Å.