Fast Neutron Effects in Tetragonal Barium Titanate

Abstract

Tetragonal BaTiO₃ is transformed into cubic BaTiO₃ as a result of irradiation with fast neutrons at a temperature of approximately 100°C. Sufficient atomic displacements are produced by bombardment with an integrated fast neutron flux of 1.8×10²⁰ n/cm² so that tetragonal single crystals (c₀=4.0349 A and a₀=3.9923 A) expand anisotropically to form perovskite‐type cubic single crystals with a₀=4.0824 A. The irradiated material remains cubic to the lowest temperature of measurement, 78°K, showing none of the low temperature phase transitions of unirradiated BaTiO₃, and after annealing at 1000°C the crystal remains cubic but with a reduced lattice parameter. X‐ray, thermal, and optical methods were employed in studying these effects.