Raman spectroscopy and microwave dielectric properties of Sn substituted SrLa₄Ti₅O₁₇ ceramics

SrLa₄Ti_5−xSn_xO₁₇ (0 ≤ x ≤ 2) ceramics were fabricated through solid state ceramic route and their microwave dielectric properties were investigated in an attempt to tune their temperature coefficient of resonant frequency (τ_f) to zero. The compositions were sintered to single phase SrLa₄Ti₅O₁₇ and SrLa₄Ti_4.5Sn_0.5O₁₇ ceramics at x = 0 and x = 0.5, and SrLa₄Ti_4−xSn_xO₁₇ along with a small amount of La₂Ti₂O₇ at x = 1. The major phase observed at x = 2 was La₂Ti₂O₇ but along with SrLa₄Ti₄SnO₁₇ and SrLa₄Ti₄O₁₅ as the secondary phases. τ_f decreased from 117 to 23.0 ppm/°C but at the cost of dielectric constant (ε_r) and quality factor multiplied by resonant frequency (Q_uf_o) which decreased from 65 to 33.6 and 11150 to 4191 GHz, respectively. The optimum microwave dielectric properties, i.e. τ_f = 38.6 ppm/°C, ε_r = 45.5 and Q_uf_o = 7919 GHz, correspond to the SrLa₄Ti_5−xSn_xO₁₇ composition with x = 1.