Browsing by Author "Schogoleva, T.V."

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Conductivity across random barrier distribution as origin of large low-frequency dielectric peak in perovskite crystals and ceramics
(1996-10) Schmidt, V. Hugo; Tuthill, G. F.; Tu, Chi-Shun; Schogoleva, T.V.; Meschia, Steven C. L.
Several perovskite crystals and ceramics show very large dielectric (ϵ′) peaks at high temperature T and low frequency ƒ. In some cases these peaks are in the cubic phase far above any ferroelectric transition. Even at the peaks, the lossy part ϵ″ is larger than the real part ϵ′. The ϵ′ vs T curves for different ƒ follow the same d.c. (low-ƒ) envelope down to some T(ƒ) below which the curve for that ƒfalls below the envelope. Similarly, the conductivity (or ϵ″) data show d.c. and a.c. (high-frequency) envelopes for which data at different ƒ overlap. As a first approximation to a crystal with random barriers impeding conductivity, a model with barriers B (in T units) every lattice constant a = 4 Å and barriers B + Δ every distance d is assumed. The model is fit to permittivity and conductivity data for a strontium titanate single crystal, and a good qualitative fit is obtained.
Random barrier height model for phase shifted conductivity in perovskites
(1997) Schmidt, V. Hugo; Tuthill, G. F.; Tu, Chi-Shun; Schogoleva, T.V.; Meschia, Steven C. L.
A large dielectric permittivity peak which occurs at low frequency and high temperature in many perovskite crystals and ceramics, and an associated difference in dc and ac conductivity, is attributed to phase shifted conductivity resulting from mobility barriers of different heights. A model is developed which has intrinsic barriers, and higher and more widely spaced extrinsic barriers, and special cases are examined. Model predictions show good agreement with experimental results of Stumpe, Wagner, and Bäuerle for an SrTiO3 single crystal 1.02 mm thick. The additional peaks seen by them at higher temperature for a crystal 0.24 mm thick are qualitatively accounted for by adding a third set of still higher barriers with spacing equal to the crystal thickness.