New high temperature dielectrics: Bi-free tungsten bronze ceramics with stable permittivity over a very wide temperature range

High relative permittivity, epsilon(r), over a very wide temperature range, -65 degrees C to 325 degrees C, is presented for ceramics designed to be compatible with base metal electrode multilayer capacitor manufacturing processes. We report a >= 300 degrees C potential Class II capacitor material, free from Bi or Pb ions, developed by doping Sr2NaNb5O15 with Ca2+, Y3+ and Zr4+ ions, according to the formulation Sr2-2zCazYzNaNb5-zZrzO15. For sample composition z = 0.025, epsilon(r) values are 1565 +/- 15 % (1 kHz) from -65 degrees C to 325 degrees C. At a slightly higher level of doping, z = 0.05, epsilon(r) values are 1310 +/- 10 % from -65 degrees C to 300 degrees C. Values of the dielectric loss tangent, tan delta are <= 0.025 from -60 degrees C to 290 degrees C, for z = 0.025, with tand increasing to 0.035 at 325 degrees C. Microstructural analyses exclude coreshell mechanisms being responsible for the flattening of the epsilon(r) -T response.