Rheology and microstructure of (Ca0.9,Sr0.1)TiO3 perovskite deformed in compression and torsion

Abstract

Polycrystalline samples of (Ca0.9,Sr0.1)TiO3 were synthesized from high‐purity oxides yielding samples with <1% porosity and grain sizes between 10 and 100 μm. These samples were used to study the rheological properties of the tetragonal and cubic phases of (Ca,Sr)TiO3. Data from compression experiments performed over a temperature range spanning the tetragonal to cubic phase transition show a change from a power law rheology at high stresses and large grain sizes to a linear‐viscous rheology at low stresses and small grain sizes. The best fit flow law is = 100.6σ5.3 exp(−521 kJ mol−1/RT) + 108.4 (σ/z1.4)exp(−627 kJ mol−1/RT), where z (m) is the grain size parameter which includes the median grain size and the standard deviation of the grain size distribution and σ is in MPa. Microstructures from of both torsion and compression experiments point to grain boundary and cooperative grain boundary sliding accommodating ∼80% of the sample strain in both the power law and linear viscous fields. Misorientation axes align parallel to the kinematic axis of the imposed deformation in both compression and torsion tests. The crystallographic preferred orientations (CPO) are weak for both torsion and compression experiments but point to 〈100〉pc as the dominant Burger's vectors. We propose that our samples deform by grain boundary sliding accommodated by diffusion at low stresses and small grain sizes and grain boundary sliding accommodated by dislocation creep at high stresses and large grain sizes. Such deformation mechanisms will not lead to a significant CPO and hence would not create a substantial seismic anisotropy. Under the conditions investigated, little change in rheological behavior was observed across the tetragonal to cubic phase transformation of perovskite.