Structure and Magnetic Properties of Oxygen Pressure Induced Sr_1.5La_0.5Cu_0.5Ti_0.5O_4-δ (0.0 ≤ δ ≤ 0.25)

Abstract

Sr1.5La0.5Cu0.5Ti0.5O4 - δ (0.0 ≤ δ ≤ 0.25) was investigated to isolate the trivalent state of Cu in an oxygen lattice. Sr1.5La0.5Cu0.5Ti0.5O4, which is free from CuII, was successfully prepared under 1.5 kbar of oxygen pressure. Structure refinements using X-ray and neutron diffraction patterns provided evidence to support a partial ordering between the Cu and Ti atoms in the ab-plane of Sr1.5La0.5Cu0.5Ti0.5O3.75 (δ = 0.25). In contrast, no clear evidence for long-range ordering was given in the Sr1.5La0.5Cu0.5Ti0.5O3.82 of high CuIII component. The oxygen vacancies were preferentially induced in the in-plane sites rather than the apical sites of the (Cu,Ti)O6 octahedra for all materials of different δ values. The magnetic susceptibilities of materials prepared under N2 or O2 flowing condition obeyed a Curie−Weiss law, while the oxygen pressure treated ones showed no constant magnetic moment; a gradual increase of the magnetic moment was observed upon increasing temperature. Moreover, an isotropic signal (g = 2.13, ΔH = 251 G) arising from CuIII was observed in ESR spectra of pressure treated materials. On the basis of Rietveld refinements of neutron diffraction data, iodometric titrations, magnetic susceptibility measurements, and pressure dependent ESR studies of Sr1.5La0.5Cu0.5Ti0.5O4 - δ , it is proposed that this isotropic signal be attributed to the high-spin state of CuIII (S = 1). Such a result is one of the rare examples of high-spin CuIII stabilized in copper-rich oxide.