Ferroelectricity

Effect of Sr$^{2+}$ ion substitution with trivalent ions (Sc$^{3+}$, In$^{3+}$, La$^{3+}$, Bi$^{3+}$) on its ferroelectric instability in SrTiO$_3$

N. G. Zamkova, V. S. Zhandun, V. I. Zinenko

L. V. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk

Abstract: The vibration frequencies of unstable ferroelectric and antiferrodistortion modes and the dependences of the energy on the ion displacement amplitude have been calculated within the generalized Gordon–Kim model for distortions along eigenvectors of these modes in the mixed compounds Sr$_{1-x}$A$_x$Ti$_{1-x/4}$ $\square_{x/4}$O$_3$ and Sr$_{1-y}$A$_{2y/3}$ $\square_{y/3}$TiO$_3$ (A – Sc$^{3+}$, In$^{3+}$, La$^{3+}$, Bi$^{3+}$; $\square$ is the vacancy). To compensate an excess positive charge, vacancies are introduced into the Ti$^{4+}$ or Sr$^{2+}$ site. Calculations have been performed in the “daverage” crystal approximation for impurity concentrations of 0.25 and 0.50. To this end, a set of 40 atomic superlattices with various orderings of heterovalent ions Sr$^{2+}$ and impurity A$^{3+}$ has been considered. It has been found that each impurity type, independently of charge balance, induces ferroelectric instabilities in doped compounds. In the case of doping with In$^{3+}$ and La$^{3+}$ for concentration $x$ = 0.25, the possibility of rotating the polarization vector has been shown.

Received: 12.04.2011

 English version: Physics of the Solid State, 2011, 53:11, 2290–2299

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