Structure and dielectric properties of Ln3NbO7 (Ln = Nd, Gd, Dy, Er, Yb and Y)

The structure and dielectric properties of Ln3NbO7 (Ln = Nd, Gd, Dy, Er, Yb and Y) ceramics are investigated. With decreasing ionic radius of Ln3+, the stable crystal structure of the compounds shifts from orthorhombic weberite to defect fluorite. It is experimentally observed that, with the exception of Gd3NbO7, the room temperature real part of the relative permittivity of Ln3NbO7 ceramics decreases from approximately 40 to 30 (at 1 MHz) with increasing ionic radius of Ln3+. The observed imaginary part of the relative permittivity is in order of 10−2 to 10−1 (room temperature and 1 MHz) and it is relatively stable up to 80 °C, where it increases with a rise in temperature. Interesting exceptions of these trends are Nd3NbO7 that crystallizes with a weberite-type structure and shows large positive temperature variation of the dielectric properties, and Gd3NbO7 that crystallized in a weberite related structure and displays frequency and temperature dependent dielectric relaxation behavior.