NEW PEROVSKITE OXIDES OF THE TYPE (M1/4Ln3/4)(Mg1/4Ti3/4)O3 (M = Na, Li; Ln = La, Nd, Sm): CRYSTAL STRUCTURE AND MICROWAVE DIELECTRIC PROPERTIES

New complex perovskite compounds La3/4Na1/4(Mg1/4Ti3/4)O-3(NLMT), Nd3/4Li1/4(Mg1/4Ti3/4)O-3 (LNMT) and Sm3/4Li1/4(Mg1/4Ti3/4)O-3 (LSMT) have been synthesized by solid state reaction process. Their crystal structure and microwave dielectric properties were investigated by using XRD Retiveld method, TEM, and network analyzer. All samples exhibited single perovskite phase with the same space group Pbnm (a(-)a(-)c(+)). No indication of cation ordering was found in these samples; however, the relative strength of superlattice reflections suggests that the degree of tilt of oxygen octahedra in LNMT and LSMT is higher than it is in NLMT, in agreement with Rietveld refinements of x-ray diffraction data. The dielectric permittivity decreased and Qxf value increased in the sequence of NLMT, LNMT and SLMT All samples exhibited negative value of temperature coefficient of resonant frequency (tau(f)).