Crystal structure, Raman spectroscopy and microwave dielectric properties of Ba3.75Nd9.5Ti18-z(Al1/2Nb1/2)zO54 ceramics

The influences of substitution of (Al1/2Nb1/2)(4+) on the crystal structure, Raman spectroscopy and microwave dielectric properties in Ba3.75Nd9.5Ti18O54 (BNT) ceramics were investigated in this work. The sintering samples were mainly measured by SEM, XRD and Raman spectrometer. The results showed that all Ba3.75Nd9.5Ti18-z(Al1/2Nb1/2)(z)O-54 (BNT-(AN)z) samples formed the orthorhombic tungsten-bronze type like structure. Lattice parameters of BNT-(AN) z samples were refined by Rietveld method, and unit cell volume of samples decreased as z increased. The blue shift of Raman spectral peaks was confirmed to the result of Rietveld refinement. Moreover, Raman spectra revealed that flexible oxygen octahedra networks became stressed-rigid and oxygen octahedra became more tilted, which was ascribed to Al3+ and Nb5+ occupational disorder when (Al1/2Nb1/2)(4+) substituted for Ti4+. With increase of z value, the dielectric constant (epsilon(r)) and temperature coefficient of resonant frequency (tau(f)) decreased. The BNT-(AN)2 ceramic sintered at 1375 degrees C for 4 h exhibited excellent microwave dielectric properties: epsilon(r) = 73.9, Qxf - 13,177 GHz, and tau(f) - +0.3ppm/degrees C. The relationship of the bond valence of the B-site to Raman shift of the Ag mode, dielectric constant (epsilon(r)) and tau(f) were analyzed. (C) 2017 Published by Elsevier B.V.