Lattice Energy Determination for Polycrystalline Oxide Ceramics and Single-Crystalline Counterparts

The compositional dependence of lattice energies for polycrystalline specimens of spinel ferrite systems, Zn x Co 1− x Fe 2 O 4 ( x = 0.0–0.6); slowly cooled and quenched systems of CuAl x Fe 2− x O 4 ( x = 0.0–0.6); high-energy ball milled mixed ferrite composition, Ni 0.5 Zn 0.5 Fe 2 O 4 (0–9 h); garnet system, Y 3− x Fe 5 + x O 12 ( x = 0.0–0.5); manganite perovskite system, La 1− x Ca x MnO 3 ( x = 0.0–1.0); and superconducting systems, Bi 1.7− x Pb 0.3 Al x Sr 2 Ca 2 Cu 3 O 10 ( x = 0.0–0.3), Bi 1.7− x Pb 0.3 Ga x Sr 2 CaCu 2 O 8 ( x = 0.0–0.3), and Bi 2 Sr 2 CaCu 2 O 8 +0−−5 % Ag + addition has been evaluated, making use of mean sound velocity data and employing Kudriavtsev’s approach. It is found that for all the systems, lattice energy decreases, and it is explained based on the change in structural and microstructural parameters as a function of substitution. The lattice energies for single-crystalline counterparts have been computed using four different estimation models based on Kapustinskii method, molecular volume and X-ray density, connectivity indices, and chemical hardness. The observed difference between the two has been discussed in the light of grain and grain boundary contributions and presence of pores and microcracks in polycrystalline materials. A simple model suggested for lattice energy determination for complex oxide compositions based on the oxide additivity rule was found to be quite satisfactory.