abstract
Ceramics based on (1-x)La(Mg1/2Ti1/2)O-3 (LMT)-xATiO(3) solid solutions, where A=Ca, Sr, and Ba, have been investigated to study the effect of average A-site ionic radius on structure and microwave dielectric properties. X-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy were used to study the structural changes and planar defects and thereby interpret changes in microwave properties. 1:1 rocksalt ordering between Mg2+ and Ti4+ in LMT was destroyed for all samples in which x>0.1. XRD and TEM revealed that all (1-x)LMT-xCaTiO(3) (LMTCT), xless than or equal to0.9, were distorted through a combination of antiphase and in-phase octahedral rotations (tilted). For (1-x)LMT-xSrTiO(3) (LMTST) this combination is present until x=0.5, and for x>0.5 only antiphase tilting exists. For (1-x)LMT-xBaTiO(3) (LMTBT), in-phase and antiphase octahedral distortions were only present for xless than or equal to0.3, x=0.5 was tilted in antiphase and xgreater than or equal to0.7 was untilted. The temperature coefficient of resonant frequency (tau(f)) varied linearly with relative permittivity (epsilon(r)) for LMTCT and LMTST but a discontinuity was observed for LMTBT at xapproximate to0.7, the composition at which octahedral rotations are no longer present at room temperature. Zero tau(f) was achieved at xapproximate to0.5 in all solid solution series. In general, the microwave dielectric quality factor (Qf(o)) decreased with increasing x to a minimum at x=0.5 for all solid solution series followed by an increase at x=0.7 despite epsilon(r) being higher for x=0.7 than for 0.5. Qf(o) then continued to decrease as x=1 was approached and epsilon(r) increased. (C) 2005 American Institute of Physics.
keywords
MICROWAVE DIELECTRIC-PROPERTIES; TEMPERATURE-COEFFICIENT; COMPLEX PEROVSKITES; RAMAN-SPECTROSCOPY; RESONANT-FREQUENCY; CRYSTAL-STRUCTURE; CERAMICS; SYSTEM; GRAIN; SIZE
subject category
Physics
authors
Seabra, MP; Ferreira, VM; Zheng, H; Reaney, IM
our authors
Maria Paula Seabra
Assistant Professor