Xiujie Yi

Complete set of material constants of 0.95(Na0.5Bi0.5)TiO3-0.05BaTiO3 lead-free piezoelectric single crystal and the delineation of extrinsic contributions

Lead-free piezoelectric single crystal 0.95(Na0.5Bi0.5)TiO3 (NBT)-0.05BaTiO3 was grown by top-seeded solution growth method, which has rhombohedral symmetry with composition near morphotropic phase boundary. Full set of dielectric, piezoelectric, and elastic constants for [001]c poled domain-engineered single crystal was determined. Excellent electromechanical properties and low dielectric loss (d33 = 360 pC/N, d31 = −113 pC/N, d15 = 162 pC/N, k33 = 0.720, kt = 0.540, and tan δ = 1.1%) make it a good candidate to replace lead-based piezoelectric materials. The depolarization temperature (Td = 135 °C) is the highest among all NBT-based materials and its electromechanical coupling properties are very stable below Td. Extrinsic contributions to piezoelectric properties were investigated by Rayleigh analysis.

The elastic and piezoelectric properties of tungsten bronze ferroelectric crystals (Sr0.7Ba0.3)2NaNb5O15 and (Sr0.3Ba0.7)2NaNb5O15

The elastic and piezoelectric constants of tungsten bronze ferroelectric crystals (Sr0.7Ba0.3)2NaNb5O15 (SBNN70) and (Sr0.3Ba0.7)2NaNb5O15 (SBNN30) are determined by using the ultrasonic and resonance methods. The measured results show that these single crystals have larger dielectric constant and good piezoelectric property compared to other known lead-free perovskite ferroelectric crystals. The measurements show that the SBNN70 has larger dielectric and piezoelectric constants than SBNN30 since the former is near the morphotropic phase boundary composition. Our results confirmed that the SBNN single-crystal system is another good candidate as lead-free piezoelectric and dielectric materials.

Structural, dielectric and optical properties of barium strontium sodium niobate (Sr0.7Ba0.3)2NaNb5O15 single crystals

Barium strontium sodium niobate (Sr0.7Ba0.3)2NaNb5O15 (SBNN70) crystals were grown by the Czochralski method. X-ray energy dispersive spectrometry showed that SBNN70 crystals have a stoichiometric composition nearly identical to the starting materials. X-ray diffraction of crushed powder indicated that the SBNN70 crystals are orthorhombic with a = 1.2748 nm, b = 1.1402 nm and c = 0.3898 nm. The measured temperature dependence of dielectric constants showed strongly anisotropic relaxor behaviour. The Curie temperature of the SBNN70 crystals is 186.7uC, which is 116uC higher than that of the (SrxBa1−x)5Nb10O30 (SBN) crystal. The transmissivity and refractive index of [001] oriented SBNN70 single crystals were measured, and a deep energy level of 3.54 eV was found. The SBNN70 crystal has better than 70% optical transmittance for wavelengths above 500 nm. The refractive index of SBNN70 is 2.004 at 632.8 nm, which is lower than 2.3117 for SBN crystals.

Analysis of optical waveguide formation in Er:NaY(WO4)2 crystal by MeV He+ ion implantation

Abstract Tetragonal scheelite-like single crystals Er:NaY(WO4)2 (Er:NYW) have been grown along its 〈1 0 1〉 direction by using RF-heating Czochralski (CZ) method. A planar optical waveguide in the as-grown Er:NaY(WO4)2 crystal was formed by 2.6 MeV He+ ions implantation with dose of 1.5×10 16 ions / cm 2 at room temperature. Using the prism coupling technique, the dark modes were measured: four TE modes and five TM modes were observed in the waveguide. Using the reflectivity calculation method (RCM), the refractive index profiles were reconstructed and analyzed before and after the optical waveguide was annealed at 300 °C for 30 min. The energy loss was simulated by the transport of ions in matter (TRIM) code, and the results were investigated in comparison with the refractive index profile in the waveguide.