KNbO3undergoes the phase transformations cubic (Pm3m) →tetragonal (P4mm2) →orthorhombic (Bmm2) at 438° C and 234° C respectively. The cubic →tetragonal transformation is accompanied by a paraelectric →ferroelectric phase transition in the crystal. It is preceded by the appearance of microdomains at 440° C and occurs with characteristic features of a first-order displacive transformation (temperature hysteresis, temperature-dependent growth and orientation relationship) with the orientation relationship (I10)c(l10)tand (001)c(001)tOn the other hand, the tetragonal →orthorhombic phase transformation takes place at exactly 234° C with a front that swept through the thin foil once the transformation was initiated. It occurs with the orientation relationship [001 [coand (100)t(100)oThe cubic-to-tetragonal transformation involves a purely dilatational mechanism along the principal axes of the cubic phase while the tetragonal-to-orthorhombic transformation involves a shear along the diagonal of the tetragonal phase.
ASJC Scopus subject areas
- Condensed Matter Physics