Dielectric properties of SrTiO3glass-ceramics

Strontium titanate glass-ceramics, prepared by the crystallization of strontium titanate-aluminosilicate glasses have been investigated for possible application as low-loss dielectric materials at microwave and millimeter wave frequencies. Under suitable crystallization conditions, these glass-ceramics exhibit temperature compensated dielectric permittivity, a consequence of the balance between the negative temperature coefficient of the SrTiO3 crystalline phase and the positive temperature coefficient of the residual aluminosilicate glass phase. Temperature coefficients of less than 10 ppm/°C with dielectric constants in the range of 16–18 have been achieved over a temperature range of -55 to 125°C. Dielectric losses at frequencies up to 4MHz are extremely low (tan δ < 0·0005). However, dielectric measurements in the range of 100–1000MHz have shown that the losses increase as the frequency approaches the millimeter wave region, indicating that these glass-ceramics might not be acceptable as millimeter wave dielectrics.