Composite Dielectric Ceramics Based on BaO–Ln2O3–TiO2 (Ln = Nd, La)

Abstract

BaLa₄Ti₄O₁₅ (BLT) is a hexagonal perovskite-related compound with a temperature coefficient of resonant frequency (τ_f) of -2 ppm/°C, relative permittivity (ε _r)∼44 and figure of merit (Q·f)∼44000 GHz. Ba₄Nd_9.333Ti₁₈O₅₄ (BNT) has a tungsten-bronze-related structure with ε _r∼78, Q·f≈11000 GHz and τ_f of +47 ppm/°C. The microstructures and microwave dielectric properties of xBNT–(1-x)BLT (0≤x≤1) composite ceramics have been studied. X-ray diffraction analysis and scanning electron microscopy revealed that there was limited inter-reaction between the two phases and that samples were composed largely of BNT and BLT, although some deterioration in measured ε _r with respect to calculated values was observed. The optimum compositions were x=0.55 and 0.75 for which ε _r∼63, τ_f∼-20 ppm/°C and Q·f>10,000 GHz.