Spontaneous strain of conductive strontium titanate Sr1− x La x TiO3 measured by using X-ray topographic domain contrast

We have measured the spontaneous strain c/a − 1 of the antiferrodistortive phase transition in the conductive strontium titanates Sr1− x La x TiO3 with x = 0, 0.005, 0.010, and 0.050 by using X-ray topographic domain contrast. We have found that the substitution of a small amount of La3+ ions into SrTiO3 leads to the large increase of the phase transition temperature T a, the saturated spontaneous strain (c/a − 1)s, and the saturated order parameter ϕ s. The values of T a and (c/a − 1)s of Sr0.95La0.05TiO3 are twice as large as those of SrTiO3. These findings indicate that the large increase of T a, (c/a − 1)s and ϕ s are not caused by the doped conduction electrons, but by the crystal structure change, due to the substitution of La3+ ions into Sr2+ sites.