RESUMEN
Domain walls in Cu-Cl boracite develop as a consequence of an improper ferroelastic, improper ferroelectric transition, and have attracted close interest because some are conductive and all can be mechanically written and repositioned by application of an electric field. The phase transition and its associated dynamical properties have been analysed here from the perspective of strain and elasticity. Determination of spontaneous strains from published lattice parameter data has allowed the equilibrium long-range order parameter for F [Formula: see text]3c â Pca21 to be modelled simply as being close to the order-disorder limit. High acoustic loss in the cubic phase, revealed by resonant ultrasound spectroscopy, is consistent with the presence of dynamical microdomains of the orthorhombic structure with relaxation times in the vicinity of â¼10-5-10-6 s. Low acoustic loss in the stability field of the orthorhombic structure signifies, on the other hand, that ferroelastic twin walls which develop as a consequence of the order-disorder process are immobile on this time scale. A Debye loss peak accompanied by â¼1% elastic stiffening at â¼40 K is indicative of some freezing of defects which couple with strain or of some more intrinsic freezing process. The activation energy of ⩾â¼0.01-0.02 eV implies a mechanism which could involve strain relaxation clouds around local ferroelectric dipoles or freezing of polarons that determine the conductivity of twin walls.
RESUMEN
An applied electric field can reversibly change the temperature of an electrocaloric material under adiabatic conditions, and the effect is strongest near phase transitions. We demonstrate a giant electrocaloric effect (0.48 kelvin per volt) in 350-nanometer PbZr(0.95)Ti(0.05)O3 films near the ferroelectric Curie temperature of 222 degrees C. A large electrocaloric effect may find application in electrical refrigeration.
RESUMEN
This paper describes the design, construction, and performance of a piezoelectric motor that uses the travelling B08 mode of an 80-mm diameter circular membrane to drive a rotor by frictional contact. The motor is of a thin planar design, giving high torque of up to 0.33 Nm at low speed and has been developed as a design that can be made with lithographic techniques for miniaturization. Investigations of the free stator with a vibration pattern imager and impedance analyzer gave the resonance frequency, mode, and electromechanical coupling of the stator. Motor speed as a function of frequency for a constant voltage and performance charts of speed, output power, and efficiency against torque are presented for a particular input voltage and rotor pre-load. The effects of two different lead zirconate titanate (PZT) ring dimensions have been investigated. Excitation of the B09 mode has been observed, incommensurate with the piezoelectric excitation of the stator. This is discussed with relation to edge-clamping of the stator. Single standing wave motoring was observed, believed to arise from asymmetry of the stator and its perturbation of the B08 resonance mode. Sources of power loss, including frame vibration and friction interface slip, are considered and discussed.
RESUMEN
Crack-free and dense PbTiO(3) films 1-2 mum thick were prepared by spinning a sol-gel derived solution onto an appropriate substrate, and firing and annealing the film at temperatures of 750-800 degrees C. The electrical properties of the films were studied as a function of temperature, frequency, and DC bias. Also, crack-free films of Pb(Sc(0.5)Ta(0.5))O(3) with an average grain size of 0.4 mum were prepared using a novel two-stage process. Films 4 mum thick had moderately high relative permittivities, low dissipation factors, and high resistivity.
