Local structure and electron spin resonance of copper-doped SrTiO₃ ceramics

Abstract

We report X-ray diffraction and electron spin resonance (ESR) measurements of the effect of SrTiO₃ ceramics doping using Cu²⁺ ions. ESR measurements reveal two kinds of Cu²⁺ centers in weakly (0.2–0.5 mol% Cu) doped SrTiO₃. Both kinds of centers have been attributed to Cu²⁺ at octahedral Ti sites and possibly associated either with a nearest-neighboring oxygen vacancy (center #1) or some other positively charged defect (center #2). The ESR spectra of the above centers are described by the following spin Hamiltonian parameters: g _‖ = 2.263(1), g _⊥ = 2.041(1), A _‖ = 170(1) × 10⁻⁴ cm⁻¹, A _⊥ = 27(1) × 10⁻⁴ cm⁻¹ (center #1) and g _‖ = 2.334(1), g _⊥ = 2.059(1), A _‖ = 137(1) × 10⁻⁴ cm⁻¹, A _⊥ ≈ 0(1) × 10⁻⁴ cm⁻¹ (center #2). For copper concentration larger than 2 mol%, the antiferromagnetic SrCu₃Ti₄O₁₂ (SCTO) phase has been detected by both X-ray diffraction and ESR. Its volume increases with increase of Cu concentration reaching about 17 % at Cu doping of 20 mol%. The composite SrTiO₃–SCTO ceramics exhibits substantial magnetocapacitance effect, which could be enhanced by electrostriction of SrTiO₃.