Correlation between structures and microwave dielectric properties of Ba3.75Nd9.5-xSmxTi17.5(Cr1/2Nb1/2)0.5O54 ceramics

In this study, the influences of substitution of Sm3+ for Nd3+ on the crystal structure, Raman spectroscopy and microwave dielectric properties in Ba3.75Nd9.5Ti17.5(Cr1/2Nb1/2)0.5O54 (BNTCN) ceramics were investigated. The XRD results showed that all Ba3.75Nd9.5-xSmxTi17.5(Cr1/2Nb1/2)0.5O54 (BNTCN-Sx) samples were crystallized as the orthorhombic tungsten-bronze type like structure. The unit cell volume of samples decreased as x increased, and the blue shift of Raman spectral peaks (Ag(1) and Bg) also confirmed this result. Moreover, the increase of tilt angles indicated that more and more oxygen octahedra became more tilted, consequently leading to the decrease of temperature coefficient of resonant frequency (τf) with increase of x value. The packing fraction and Q×f value of BNTCN-Sx ceramics reached the maximum value, whereas the FWHM of Ag(1) and internal strain η reached the minimum value at x = 3. The low internal strain resulted from stability of the crystal structure, which was conducive to improvement of Q×f value in the BNTCN-Sx ceramics. At last the BNTCN-Sx ceramics sintered at 1380 °C for 4 h exhibited excellent microwave dielectric properties: εr = 83.6, Q×f = 11,597 GHz, and τf = +1.3 ppm/°C when x = 4.