New Phases of Sr₂Ta₂O₇ and Sr₂Nb₂O₇ Found by Electron Microscopy and Diffraction

Abstract

New low temperature phases of Sr 2 Ta 2 O 7 and Sr 2 Nb 2 O 7 were found by electron microscopy. Sr 2 Ta 2 O 7 undergoes a structural phase transition at about 170°C to a superlattice structure belonging to the monoclinic system with space group P2 1 / m , accompanying the appearance of characteristic twin and antiphase domains. Sr 2 Nb 2 O 7 has an incommensurate phase below about 220°C with an irrational lattice modulation in the [100] direction and an intricate fine domain-like texture.