Transitions in Morphotropic PMN-PT Single Crystals

Single crystals in the relaxor-ferroelectric lead magnesium niobate (PMN)-lead titanate (PT) and lead zinc niobate (PZN)-lead titanate (PT) systems provide a significant advantage for detecting and classifying objects in littoral waters. Their extremely large electromechanical coupling factor (k ₃₃ > 0.90) and piezoelectric coefficient (d ₃₃ > 1000 pC/N) offer both broadband and high acoustic source level capabilities. Two different transition pathways can be accessed in a morphotropic PMN-0.30PT composition. Resonance experiments on a length extensional bar fabricated from a multi-domain, [001] oriented and poled PMN- 0.30PT crystal revealed a monotonically decreasing Young's modulus as a function of temperature with a sudden stiffening near 85°C corresponding to a ferroelectric rhombohedral (F _R )-ferroelectric tetragonal (F _T ) transition. Quasi-static, zero field stress-strain response revealed an elastic instability of the F _R near 30 MPa compression. This instability is attributed to a ferroelectric rhombohedral (F _R )–ferroelectric orthorhombic (F _O ) transition. A dc bias field of 0.59 MV/m stabilized the F _R state up to 40 MPa compressive stresses. The implications of these results on sonar projector design and performance will be discussed.

Keywords:

• Single crystals
• phase transition
• large electromechanical coupling

Acknowledgments

We thank the Office of Naval Research for the financial support of this work.