Electric Field Effect in ESR Spectra of Fe³⁺ and Mn⁴⁺ Centers in Thin SrTiO<inf>3</inf> Plates

Abstract: The electric field effect in electron spin resonance spectra of Fe3+ and Mn4+ impurity ions in thin oriented single-crystal plates of strontium titanate has been studied; the crystal structure of these samples at T > 105 K is tetragonal (i.e., differs from both cubic and antiferrodistortive tetragonal structure that is inherent in SrTiO3 at T < 105 K). It is shown that the electric field effects for the investigated centers are quadratic with respect to the applied field and have identical signs and orders of magnitude, thus indicating a nonpolar character of the observed high-temperature tetragonal state. An analysis of the dependences of the axiality value on the applied field indicates that the electric field effect is not related to electrostriction and caused by modification of the wave function of the ground state of impurity centers

Experimental evidences of the shape-induced structural distortion of SrTiO3 single crystals from impurity Mn4+ ions electron paramagnetic resonance

A study of high-quality SrTiO3 single crystals doped with the Mn4+ ions in the cubic phase (T > 105 K) with X-band electron paramagnetic resonance reveals direct correspondence between a shape of a sample and magnetic anisotropy of the impurity Mn4+ centers. In particular, for a sample with the shape of a square base rectangular prism, a size of (a × a × h) and faces perpendicular to the crystallographic directions, zero-field splitting parameter D is approximately proportional to (a / h − 1) quantity. Temperature dependence of D indicates that this peculiar symmetry lowering is a feature characteristic for the cubic Fm3m phase of the strontium titanate. Diminishing of the D value with the decrease of the surface roughness for a thin (001)-oriented SrTiO3:Mn platelet shows that the observed effect originates from the sample surface

Association of impurities and vacancies in copper doped potassium tantalate crystals studied by EPR

he high temperature behavior of Electron Paramagnetic Resonance (EPR) signals of Cu2+ centers and Cu2+-Cu2+ exchanged coupled pair centers in potassium tantalate (KTaO3, and related K1-xLixTa1-yNbyO3) single crystals has been studied. EPR signals were observed in the range of 300-1000 K. The dynamic behavior of oxygen vacancies and the influence of its on Cu2+ ions EPR spectra were found. A model for divalent impurity ions in the potassium tantalate crystal is proposed

Manganese oxide nanoparticles in SrTiO3:Mn

This is an experimental work, devoted to the study of defects in insulators. In particular it is devoted to the study of manganese insertion in strintium titanate matrix by electron paramagnetic resonance (EPR). Weakly concentrated “as-grown” and reduced SrTiO3 :Mn crystals and ceramics are investigated by means of EPR to get new insights concerning the Mn substitution in the strontium titanate structure. The temperature dependence of Mn2+ and Mn4+ EPR spectra strongly indicates the formation of MnO2 or MnO small particles to be the favored configuration for the Mn insertion in SrTiO3. Only a part of manganese ions incorporates into the crystal lattice in B position as Mn4+. This work was developed in the frame of a collaboration with IOFFE INSTITUTE of Russian Academic Science of San Petersburg

Divalent impurity ions in potassium tantalate studied by EPR

EPR results of potassium tantalate single crystals eloped by Co2+ ions as well as new results of our continuous studies of KTaO3. Cu single crystal have been submitted. Divalent impurity ions substitute for Ta5+ in the octahedron position in the KTO3 crystal and oxygen vacancies are required to compensate the extra charge of Ta5+. The Cu2+ ions associated with oxygen vacancies form only axial centres (included exchange coupled pair centre), the symmetry axes being along cubic directions. New axial centre of Co2+ in the crystal of KTaO3: Co have been studied