Abstract
Electron magnetic resonance (EMR) spectra of Cr3+ ions in samples of chromium-doped strontium titanate (SrTiO3) have been studied at room temperature for chromium concentrations between 0.20 and 1.00 mol%. According to previous studies, chromium substitutes Ti4+ sites in the lattice and its preferred valence state is Cr4+, which is EMR silent in the X-band, but the trivalent state can be produced by illumination or codoping with Nb. In the present work, the codoping method was used; the results show the electron magnetic resonance linewidth of the Cr3+ spectrum increases with increasing chromium concentration and that the range of the exchange interaction between Cr3+ ions is about 0.96 nm.
Highlights
Strontium titanate (SrTiO3) is a high dielectric constant ceramic material with several industrial applications[1,2,3,4], such as memory devices, oxygen sensors, electro-optical devices and flexible dielectric waveguides, whose electrical properties can be changed by the presence of transition metal and rare earth impurities such as iron and gadolinium[5,6]
The chromium/niobium doped samples used in this study were prepared from high-purity SrTiO (Aldrich, 99%), Cr2O3 (Aldrich, 99.9%) and Nb2O5 (Aldrich, 99.99%) powders by grinding them together and firing the mixture for 24 hours at 1200 °C in air
Since niobium was intended to act as an electron donor, we used equal molar concentrations of Cr and Nb in each sample
Summary
Strontium titanate (SrTiO3) is a high dielectric constant ceramic material with several industrial applications[1,2,3,4], such as memory devices, oxygen sensors, electro-optical devices and flexible dielectric waveguides, whose electrical properties can be changed by the presence of transition metal and rare earth impurities such as iron and gadolinium[5,6]. We study the effect of chromium concentration on the EMR spectrum of Cr3+ in polycrystalline SrTiO3 codoped with chromium and niobium. The importance of this investigation is twofold. Once the effects of chromium concentration on the spectrum are known, it becomes possible to use EMR results to study the effects of other impurities[7,8,9] on the valence state of the chromium ion in SrTiO3. Analysis of the EMR spectrum of single-crystal chromium-doped strontium titanate[13] shows that Cr4+ ions substitutionally replace titanium ions in the lattice. The spectrum of Cr3+ under illumination consists of a central line (g ≈ 1.978) due to 50Cr, 52Cr and 54Cr and a hyperfine quartet due to the 53Cr isotope[13]
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