High performance piezoelectric crystal cut designed in LiNbO3 for high temperature acoustic emission sensing application

Lithium niobate (LiNbO3, LN) is a kind of multifunctional crystal material. In this study, an optimum piezoelectric crystal cut (XZt/28°) with central resonance frequency of 150 kHz and stable electro-elastic...

Flexoelectric effect on thickness-shear vibration of a rectangular piezoelectric crystal plate

Thickness-shear (TSh) vibration of a rectangular piezoelectric crystal plate is studied with the consideration of flexoelectric effect in this paper. The developed theoretical model is based on the assumed displacement function which includes the anti-symmetric mode through thickness and symmetric mode in length. The constitutive equation with flexoelectricity, governing equations and boundary conditions are derived from the Gibbs energy density function and variational principle. For the effect of flexoelectricity, we only consider the shear strain gradient in the thickness direction so as to simply the mathematical model. Thus, two flexoelectric coefficients are used in the present model. The electric potential functions are also obtained for different electric boundary conditions. The present results clearly show that the flexoelectric effect has significant effect on vibration frequencies of thickness-shear modes of thin piezoelectric crystal plate. It is also found that the flexoelectric coefficients and length to thickness ratio have influence on the thickness-shear modes. The results tell that flexoelectricity cannot be neglected for design of small size piezoelectric resonators.

Development of in situ measurement of solid-state deformation in a large anvil press utilizing a piezoelectric crystal

<p>In situ measurement of solid-state deformation in a large volume press has historically required use of neutron and x-ray scattering facilities. The lack of widespread availability of these facilities has limited the abilities of researchers to measure in situ deformations on a regular basis. We have developed an assembly that utilizes a piezoelectric crystal within a typical large volume press assembly in a 6-axis press at pressures up to 5 GPa. The basic design of the assembly can be applied to multiple assembly sizes for a wide range of possible pressures. The piezoelectric crystal is a round disk, <1 mm in diameter, that is sputter coated with Au. Copper wires are placed through drilled holes in the side of the assembly, one connected to each side of the disk. The crystal generates a voltage across the two faces when a deviatoric stress is applied that is measured and plotted in real-time during the experiments. The voltage is then used to calculate strain and strain-rate in uniaxial compression. Using the known equation of state of the piezoelectric crystal, such as quartz or gallium orthophosphate, the stresses responsible for the strain can be calculated. Thus, we can measure the stress and strain regime of simple deformation within an assembly in situ in real-time during the deformation. We have measured strain-rates as low as 10<sup>-7 </sup>s<sup>-1 </sup>over a greater than 30-minute timescale. The total strain on the assembly can be measured by the total distance advanced by the press piston, which must be accommodated. Comparing the differences in strain accommodated by the piezoelectric crystal between separate experiments allows us to infer the strain accommodated by the sample under investigation.</p><p>Current limitations in measuring lower strain-rates are charge-leakage around the piezoelectric crystal causing a voltage drift during measurements and limitations in high-temperature experiments due to phase transitions during heating in the piezoelectric crystals to phases that are not piezoelectric. Future work will concentrate on finding a suitable, high-resistance material to place around the piezoelectric crystal to limit charge leakage and designing the assembly such that the piezoelectric crystal experiences lower temperature during heating than the sample to avoid phase transitions in the crystal.</p>

Temperature-dependent behaviours of electro-elastic constants for the Bi2ZnB2O7 piezoelectric crystal

The BZBO crystals were found to present good temperature stability of elastic compliances.

Spontaneous Growth of CaBi4Ti4O15 Piezoelectric Crystal Using Mixed Flux Agents

The bismuth layer-structured ferroelectrics (BLSFs) materials have potential for high-temperature piezoelectric applications. Among these piezoelectric materials, the CaBi4Ti4O15 (CBT) piezoelectric ceramic with a high decomposition temperature of about 1250 °C attracts a lot of attention. Achieving a CBT single crystal is a significant way to improve its piezoelectric properties. For this purpose, the flux system for growing CBT crystal was explored in this study. The optimum flux composition ratio was found to be PbO:B2O3:CBT = 3:3:1 in mol%, where the PbO–B2O3 mixtures were used as a flux system. Millimeter size flake-shaped CBT crystals were obtained using the spontaneous growth process for the first time. The relationship between the crystal structure and flake growth habit was analyzed. In addition, the bandgap was evaluated by the combination of transmittance spectrum and first-principle calculations. Besides, the piezoelectric property was predicted from the perspective of polyhedral distortion, which indicated the potential of CBT crystal for piezoelectric applications.