Structure and properties of La(Zn_1/2Ti_1/2) O₃

(La,Nd)(Zn,Mg)_0.5Ti_0.5O₃ compounds are of great interest for microwave dielectric applications, although the structure of some of these complex perovskites is still uncertain. The perovskite tolerance factors in this family of compounds range from 0.916 to 0.952, suggesting a very high degree of tilting in the oxygen octahedra for compositions throughout the system. The effects of this tilting in La(Zn_0.5Ti_0.5)O₃, for example, have been observed in this study by transmission electron microscopy in the form of 1/2{3 1 1}_c and 1/2{1 3 1} α superlattice reflections and 1/2(2 3 1)_c γ reflections corresponding to anti-phase and in-phase tilting, respectively. Systematic La⁺³ displacement was also detected by the appearance of {h + 1/2, k, l}_c (β) reflections. Reflections of the type 1/2{1 1 1}_c in neutron diffraction patterns indicate 1:1 cation ordering on the B-site. Electrical tests show no piezoelectricity in La(Zn_0.5Ti_0.5) O₃, indicating a centrosymmetric point group. Rietveld refinements of neutron diffraction patterns indicate that the space group is P2₁/n, with lattice constants a = 7.8943 Å, b = 5.5959 Å, c = 5.5805 Å, and β = 90.0291°.