Directionally dependent ferroelectric phase transition order of anisotropic epitaxial BaxSr1−xTiO3 thin films

Abstract

Epitaxial Ba0.5Sr0.5TiO3 thin films were grown by pulsed-laser deposition on (100) LaAlO3 substrates in two distinct strain states, c∕a>1 and c∕a<1. X-ray diffraction measurements over the temperature range of 20°Cto−120°C showed that the change in the c∕a ratio with decreasing temperature was discontinuous and positive for the film with c∕a>1, and continuous and negative for the film with c∕a<1. These symmetry changes in the c∕a ratio with temperature were correlated with measurements of the in-plane dielectric properties, and showed that the polarization in these two types of structures has characteristically different behavior that is highly directionally-dependent.

Crystallographic and dielectric properties of highly oriented BaTiO3 films: Influence of oxygen pressure utilized during pulsed laser deposition

“…4 between 15 and 20 mTorr is particularly interesting since it reflects the oxygen pressure range where the c/a ratio decreases below 1. A similar shift of Ba x Sr 1−x TiO 3 (BST) films on MgO substrates has also been reported nearly reaching the cubic phase at a specific oxygen pressure [22][23][24]. Preferred orientation of sputter deposited BTO thin films on amorphous quartz, with changes from (100)/(001) to (110) with increasing process pressure [17] has also been observed.…”

“…One demonstrated means for tuning the lattice parameter of perovskite thin films is to vary the oxygen partial pressure during film growth [17][18][19][20][21][22][23]. Deposition kinetics [17] and the resultant stoichiometry [22] of the grown films have been proposed as explanations for this phenomenon.…”

“…As a result of the shift in lattice parameter mismatch between film and substrate, the stress state can be changed. This, in turn, can result in a change in preferred orientation [17,18,20,22,23] and even the crystal phase of the film, e.g., the paraelectric or ferroelectric phase, depending on working pressure [24].…”

Phase diagram and dielectric behavior of Ba0.6Sr0.4TiO3 thin films grown on orthorhombic substrates

“…In experiment, Simon et al [18,19] investigated the permittivity of Ba 0.6 Sr 0.4 TiO 3 films grown on orthorhombic NdGaO 3 substrates by pulsed laser deposition. Bellotti et al [20,21] studied inplane anisotropy in BST films and SrTiO 3 films.…”

“…Moreover, Chen et al [14] introduced spontaneous strain of film which roots in spontaneous polarization to study nonlinear electric field dependence of piezoelectric response in epitaxial ferroelectric PZT thin films. Recently, experiments and theories pay more attention to the films which are not grown on cubic substrates [15][16][17][18][19][20][21]. In theory, Zembilgotov et al [16] firstly considered phase diagrams of a single-domain PT film and a Pb 0.35 Sr 0.65 TiO 3 film grown on orthorhombic substrates and predicted the equilibrium polarization states of thin films.…”