Improved microwave dielectric properties of LaZn1/2Ti1/2O3 through Y3+ substitution

Abstract

LaZn1/2Ti1/2O3 is a double perovskite with promising microwave dielectric properties for applications towards dielectric resonators and antennas. Its dielectric properties can be enhanced through the substitution of suitable ions in either A- or B-sites. In this paper, we report a significant improvement in the quality factor (Q) by substituting Y3+ in the La site with a marginal reduction in dielectric constant (εr). A single phase is confirmed in XRD indicating the formation of La1-xYxZn1/2Ti1/2O3 (0 ≤ x ≤ 0.25) solid solutions. The substitution results in an expansion of lattice along the b direction while there is a contraction in both a and c directions, leading to a reduction in unit cell volume. The dielectric constant, εr, is observed to reduce from 33.4 to 29.6 due to the polarizability of A-site atoms. The temperature coefficient of resonant frequency (τf) increases with an increase in x which does not appear to correlate with reducing tolerance factor (t). This non-conventional behaviour of τf in this perovskite based solid solutions brings bond valence of O site (VO) into picture. VO appears to show competing effect on τf. The non-monotonic behaviour is observed in Q×f with a maximum value of 41,400 GHz at x = 0.15 and a sharp decline for x > 0.15. This observation is correlated with variations in the A-site bond valence (VA) and a long-range ordering (LRO) of B-site ions. LRO is associated with Ag mode at 710 cm−1 in the Raman spectra. The low frequency (< 250 cm−1) Raman modes shift to a higher frequency with the increase in Y3+. Y3+ substitution also induces lattice distortion which is discussed in terms of variations in FWHM and relative intensity of the Raman modes.