Zhiguo Chen

Trapped thickness-twist modes in an inhomogeneous piezoelectric plate

We show the existence of certain thickness-twist modes in an unbounded, inhomogeneous piezoelectric plate of crystals with 6-mm symmetry or in polarized ceramics. The modes found are trapped, with the vibration confined to a portion of the plate. These modes are exact and satisfy the three-dimensional equations of piezoelectricity. Potentially, they can be used as the operating modes of plate resonators and acoustic wave sensors, in particular, thin film resonators of ZnO and AlN.

Precipitation of quasicrystal approximant phases in an Al–Mg–Cu–Ge alloy

Cube-shaped precipitates in the peak-aged Al–4.0Mg–1.5Cu–0.25Ge (wt.%) alloy were found to exhibit a pseudo five-fold symmetry in their electron diffraction patterns along the ⟨1u20091u20090⟩ and ⟨1u20091u20093⟩ zone axes of the Al matrix. These strengthening precipitates, designated as the Z′, possess a structure in a transition state from an icosahedral quasicrystal phase to a face-centred cubic (FCC) quasicrystal approximant phase. After prolonged ageing, the Z′ phase transforms into the FCC equilibrium Z phase having atoms in a periodic icosahedral arrangement.