Some observations on the effects of shear stress on a polymorphic transformation in perovskite-structured lead-zirconate-titanate ceramic
- Sandia National Lab., Albuquerque, NM (United States)
We performed a series of hydrostatic and constant-stress-difference (CSD) experiments at room temperature on modified lead-zirconate-titanate (PZT 95/5-2Nb) ceramic in order to quantify the influence of shear stress on the displacive, and possibly martensitic, first-order, ferroelectric/rhombohedral [r arrow] antiferroelectric/orthorhombic phase transformation. In hydrostatic compression, the transformation began at approximately 260 MPa and was incompletely reversed upon return to ambient conditions. Strains associated with the transformation were isotropic, both on the first and subsequent hydrostatic cycles. Results for the CSD tests were quite different. First, the confining pressure and mean stress at which the transition begins decreased approximately linearly with increasing stress difference. Second, we observed that the rate of transformation apparently decreased with increasing shear stress and the accompanying purely elastic shear strain. This result contrasts with the almost universal assertion that shear stresses accelerate reaction and transformation kinetics. Finally, strain was not isotropic during the transformation: axial strains were greater and lateral strains smaller than for the hydrostatic case, though volumetric strain behavior was comparable for the two types of tests. However, this last effect does not appear to be an example of transformational plasticity but, rather, a one-time' occurrence: no additional unexpected strains accumulated during subsequent cycles through the transition under nonhydrostatic loading. If subsequent hydrostatic cycles were performed on samples previously run under CSD conditions, strain anisotropy was again observed, indicating that the earlied superimposed shear stress produces a permanent mechanical anisotropy in the material. The mechanical anisotropy probably results from a crystallographic preferred orientation that developed during the transformation under shear stress. 59 refs., 9 figs.
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 6647658
- Journal Information:
- Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 98:B2; ISSN JGREA2; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360602* -- Other Materials-- Structure & Phase Studies
ANISOTROPY
BEHAVIOR
CERAMICS
COMPRESSION
ELEMENTS
KINETICS
LEAD
LEAD COMPOUNDS
LOADING
MATERIALS HANDLING
MECHANICAL PROPERTIES
METALS
MINERALS
ORIENTATION
OXIDE MINERALS
OXYGEN COMPOUNDS
PEROVSKITE
PEROVSKITES
PHASE TRANSFORMATIONS
PLASTICITY
PZT
SHEAR
SHEAR PROPERTIES
STRAINS
STRESSES
TITANATES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
ZIRCONATES
ZIRCONIUM COMPOUNDS