New powellite type oxides in Ca-R-Nb-Mo-O system (R=Y, La, Nd, Sm or Bi) - Their synthesis, structure and dielectric properties

New complex oxides having powellite (CaMoO4) type structure in the Ca-R-Nb-Mo-O system (R=Y, La, Nd, Sm or Bi) were prepared employing the method of solid state reaction between the component oxides at high temperature (1000-1100 degrees C). The new compounds, CaRNbMoO8 (R=Y, La, Nd, Sm, Bi) are colorless and electrical insulators. The dielectric constants (K at 1 MHz) of these compounds are in the range 14-33 and K shows very little variation in the temperature range 30-100 degrees C. Their temperature coefficient of dielectric constant (TCK) is negative, which varies from -21 to -220 ppm/degrees C. (C) 2008 Elsevier B.V. All rights reserved.