AB-INITIO STUDY ON ELECTROMECHANICAL PROPERTIES OF YTTRIUM DOPED BARIUM ZIRCONATE

Yttrium doped BaZrO₃ combines a high bulk proton conductivity with good chemical stability and is thus considered a promising electrolyte material for protonic ceramic fuel cells (PCFCs), cf. [1] and references therein. Acceptor doping e.g by Y³⁺ in the Zr⁴⁺ site is accompanied with oxygen vacancy formation. The incorporation of protons into BaZrO₃:Y by hydration of oxygen vacancies then leads to the proton conductivity. In spite of its potential for PCFCs, hydrated BaZrO₃:Y is also investigated regarding its unusual electromechanical properties [2]. Due to cubic symmetry, piezoelectricity is absent in this material but electrostriction (i.e. the second order quadratic effect linking strain and electric field squared) can still be observed. Indeed, it was found that the electrostriction coefficient in BaZrO₃:Y is exceptionally high and does not follow the well-known empirical relationship between the electrostriction coefficient and the quotient of elastic compliance and dielectric constant (Newnham’s law). In fact, it was proposed [2] that BaZrO₃:Y belongs to a new class of materials that display non-classical electrostriction effects associated with a high concentration of point defects.
In this presentation, we discuss the elastic and dielectric properties of BaZrO₃:Y being calculated by means of density functional theory (DFT). Comparing experimental Young’s moduli [3] with DFT results shows good consistency, with a considerable modulus decrease with increasing Y doping. A mechanism is discussed in which the response of point defect clusters to an external electric field causes a macroscopic strain that could, in principle, explain the observed high electrostriction coefficient.

[1] K. D. Kreuer, Annu. Rev. Mater. Res. 33, 333-59 (2003)
[2] N. Yavo, O. Yeheskel, E. Wachtel, A. Frenkel and I. Lubomirsky, Abstract Solid State Ionics Conference, Padua, Italy (2017)
[3] I. Lubomirsky, unpublished results