Oxides and Oxide Superconductors: Elastic and Related Properties

Published

August 1, 1991

Author(s)

M Lei, H M. Ledbetter

Abstract

Using both measurements and modeling, we studied the elastic and related properties of some oxides and oxide superconductors. The polycrystal elastic constants were measured using a megahertz-frequency pulse-echo method between 295 and 4 K and corrected to the void-free state by using a model for a composite material containing spherical particles. The elastic moduli of the high-T_c superconductor Y₁Ba₂Cu₃O_τ (YBCO) were compared with that oxides, especially the perovskites BaTiO₃ and SrTiO₃, which are crystal-structure building blocks for the YBCO superconductor. The bulk moduli were also calculated using a Born ionic model with two energy terms: electrostatic (Madelung) and ion-core-repulsion. The calculated bulk modulus of YBCO, 98 Gpa, agrees well with measurement, 101 GPA. Based on monocrystal measurements combined with analysis-theory, elastic stiffnesses C_ij for orthorhombic YBCO were estimated. The bulk modulus obtained from the estimated C^ij^ by the Voigt-Reuss-Hill averaging method agrees with the monocrystal measurement. From the measured polycrystal elastic constants, the Debye characteristic temperatures, θ_D, were calculated. For YBCO, θ_D = 437 K. The electron - Phonon parameters, γ were estimated from T^c^ and θ _D using Kresin's model, which is valid for all values of γ. For YVCO, γ = 2.24. Calculating the Madelung energy allowed us to study two further features: the valence of copper and the electron hole distribution. The results show that the hole prefers the CuO₂ plane at the oxygen sites. All the results are consistent with the assumption that all copper ions have valences near +2. Using a relationship between T_{c6 and δ V}dA^, the difference in Madelung site potentials for a hole at the apical and planar oxygens, the pressure derivative and stress and stain derivatives of T_c were calculated. The results show that T_c increases with decreasing a-axis, increasing b-axis, and decreasing c-axis.

Citation

NIST Interagency/Internal Report (NISTIR) - 3980

Report Number

3980

NIST Pub Series

NIST Interagency/Internal Report (NISTIR)

Pub Type

NIST Pubs

Keywords

born model, buld modulus, Debye temperature, elastic constants, electron-phonon parameter, Kresin model, oxides, pressure derivative, superconductors

Citation

Lei, M. and Ledbetter, H. (1991), Oxides and Oxide Superconductors: Elastic and Related Properties, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD (Accessed July 27, 2024)