High temperature creep of an orthorhombic perovskite - YAlO3

Compression tests were performed on single crystals of orthorhombic perovsk ite (YAlO3) along the [110] and [100] directions at temperature of T = 1763 -1883 K (0.82-0.88 T-m) and P-total = 0.1 MPa in a controlled atmosphere of f(O2) = 10(-17)-0.02 MPa. Applied stresses were in the range of 70-300 MPa yielding strain rates of (epsilon) over dot similar to 10(-7) s(-1) to sim ilar to 10(-4) s(-1). Creep strength of YAlO3 is significantly higher than those of cubic perovskites when compared at same normalized conditions. Cre ep behaviour of YAlO3 depends on crystallographic orientation and oxygen fu gacity and can be summarized as ((epsilon) over dot (s(-1)), sigma (MPa), f (O2) (MPa), R (kJ (mol K)(-1)) and T (K)): (1) for [110] orientation: (2) f or [100] orientation: [GRAPHICS] and [GRAPHICS] (2) for [100] orientation: [GRAPHICS] Dislocation microstructures of deformed YAlO3 show marked difference from t hose of cubic perovskites. Importance of dislocation climb and splitting (d issociation) is demonstrated by TEM observations. These observations indica te that the deformation mechanisms in this orthorhombic perovskite is funda mentally different from those in cubic perovskites and therefore the result s for cubic perovskites may not be applied to the Earth's lower mantle wher e orthorhombic perovskite is considered to be the dominant phase. (C) 1999 Elsevier Science B.V. All rights reserved.