Structural and electrical properties of silver niobate and silver tantalate

Abstract

At room temperature both AgNbO 3 and AgTaO 3 possess orthorhombic multiple-cell perovskite-type structures and are isomorphous with NaNbO 3. In AgNbOa the structure changes sharply to near-tetragonal at 325 ° C., while in AgTaO3 a similar change occurs, more smoothly, at about 375 ° C. At higher temperatures a sequence of structural changes closely similar to that in :NaNbO 3 leads to a fully isotropic condition at 560 ° C. for AgNbOa and 480 ° C. for AgTaO3. The permittivity of AgNbO a shows a peak at the orthorhombic-tetragonal transition reminiscent of that normally observed at a ferroelectric or antiferroelectric Curie temperature. Weak hy.steresis and pyroelectric effects indicate a low value of spontaneous polarization. It is concluded that in AgNb03 the structural changes are probably influenced chiefly by ionic packing considerations. With AgTaO 3 the presence of free silver precluded electrical measurements, but the nature of its structure transitions and the permittivity data obtained for the solid solution AgNb0.75Ta0.e503 suggest the absence of ferroelectricity.