He-wei Wang

High-performance, high-temperature piezoelectric BiB3O6 crystals

High-performance piezoelectric materials are desirable for piezoelectric sensing applications. In this paper, piezoelectric α-BiB3O6 (BIBO) crystals were explored for high temperature sensing. Dielectric, piezoelectric and electromechanical properties were evaluated by using the impedance method, from which the piezoelectric charge coefficients were determined to be d14 = 10.9, d16 = 13.9, d21 = 16.7, d22 = 40.0, d23 = 2.5, d25 = 4.3, d34 = 18.7 and d36 = 13.0 pC/N, with corresponding piezoelectric voltage coefficients g14 = 122, g16 = 144, g21 = 225, g22 = 538, g23 = 34, g25 = 58, g34 = 165 and g36 = 121 × 10−3 V m N−1 at room temperature (RT). Of particular significance is that the receiving sensitivity of BIBO crystals was found to be 47.2 pm2 N−1, nearly one order of magnitude higher than that of LiNbO3 crystals. Moreover, the BIBO crystals were found to possess a high mechanical quality factor Qm (13 000 at RT and >1000 at 600 °C), low dielectric loss (<0.1% at RT and 15% at 600 °C and 1 kHz), high electrical resistivity (∼2.5 × 108 Ω cm at 600 °C) and high temperature stability of piezoelectric coefficients (variations <±10%). All these properties demonstrate that BIBO crystals are promising for piezoelectric sensing over a broad temperature range.

Crystal growth and characterization of CTGS and Nd:CTGS for self-frequency-doubling applications

Crystal materials with integrated functionalities are desirable for the miniaturization of future optical devices. In this paper, nonlinear optical crystals of Ca3TaGa3Si2O14 (CTGS) and Nd3+ doped CTGS (Nd:CTGS) were grown using the Czochralski pulling method and explored for self-frequency-doubling applications. Based on the refractive indexes, the optimum phase matching directions for CTGS crystals were determined for type I (38.7°, 30.0°) and type II (61.1°, 0°) orientations, with respective effective nonlinear optical coefficients on the order of 0.44 pm V−1 and 0.34 pm V−1. Self-frequency-doubling was realized in Nd:CTGS crystals [(38.7°, 30.0°) (type I)] for the first time, and 18.8 mW laser power at 533 nm was achieved.

High temperature piezoelectric single crystals: Recent developments

High temperature piezoelectric materials serving at harsh environment without failure are desired for structural health monitoring and/or non destructive evaluation of the modern aerospace structures at elevated temperatures (above 600°C). In this report, different high temperature piezoelectric crystals, including the langasite (LGS) type crystals and GaPO4 in trigonal system, melilite type and fresnoite type crystals in tetragonal system, and oxyborate crystals in monoclinic system are surveyed, and their properties are compared. Among the LGS type piezoelectric crystals, the structural ordered trigonal Ca3TaGa3Si2O14 (CTGS) crystals as well as the Al substituted CTGS crystals shew relative low dielectric loss (<5%@600°C), high electromechanical coupling factor (12%∼18%@room temperature) and good temperature stability of piezoelectric properties up to 900°C, potential for usages in middle-high temperature range. Interestingly, the monoclinic RECa4O(BO3)3 (RECOB, Re: rare-earth elements) type crystal were found to own attractive dielectric, piezoelectric and electromechanical properties up to 1000°C, particularly, the YGdCOB crystals were determined to possess temperature independent behavior of piezoelectric properties (variations of piezoelectric d.26 <−5% over the tested temperature range), promising for ultrahigh temperature piezoelectric applications.

Hydrostatic piezoelectric properties of bismuth triborate crystals

In this report, the dielectric and hydrostatic piezoelectric properties of the monoclinic bismuth triborate crystals (BiB₃O₆, BIBO) were investigated at ambient temperature for potential hydrophone application. The pressure dependence of the hydrostatic charge and voltage coefficients dielectric properties (d_h and g_h), and hydrostatic figure of merit (FOM) d_h×g_h, were also studied. Results indicated that the BIBO crystals possess low dielectric loss being on the order of <;0.1% at room temperature. The hydrostatic piezoelectric coefficient d_h for BIBO crystals was experimentally obtained to be d_h =3.3 pC/N, while the piezoelectric hydrostatic coefficient g_h was obtained to be on the order of g_h =44.4×10^-3 V·m/N. Moreover, the FOM value was found to be on the order of 0.15 pm²/N, comparable to that of PMN-PT single crystals (0.12-0.78 pm²/N). In addition, the pressure coefficient a₁/d_h (1.0×10^-4 ppm/Pa) was calculated and found much lower than the reported PMN-PT single crystals (~0.001 ppm/Pa).

Single crystal growth and piezoelectric characterization of the bismuth triborate crystals

The bismuth triborate crystals BiB3O6 (BIBO) are multifunctional crystal materials with noncentrosymetric characteristics. In this paper, single crystal growth of BIBO crystals by using the top seeded solution method in a short period (within one month) was reported and the determination of the dielectric, elastic and piezoelectric constants were discussed for potential piezoelectric applications. For BIBO crystals with monoclinic symmetry, the full set of electro-elastic constants were evaluated taking advantage of the impedance method. Particularly, some parameters were obtained by designing and measuring the habitual facets of the BIBO crystals. It is interesting to find that the BIBO crystals possess high longitudinal piezoelectric coefficient d22 and shear piezoelectric coefficient d34, being on the order of 40.0pC/N and 18.7pC/N, respectively, 3-7 times that of langasite crystals, showing the advantages for applications in piezoelectric field.

Growth and piezoelectric properties of TmCOB single crystals

New rare-earth oxyborate crystals TmCOB were grown by using the Czochralski method. The piezoelectric coefficients for TmCOB were determined to be on the order of d₁₁=1.7, d₁₂=3.8, d₁₃=-4.2, d₁₅=-0.92, d₂₄=4.9, d₂₆=7.8, d₃₁=-0.75, d₃₂=-2.4, d₃₃=2.2 and d₃₅=-5.2 pC/N. The temperature dependence of electro-elastic propertieswereinvestigated from 20 to 900°C, where the temperature coefficients of the elastic compliances (s^E₂₂, s^E₃₃ and s^E₆₆) were foundto be ranged from 146 to223 ppm/°C for TmCOB crystals. Particularly, the electromechanical factor k₁₂ was evaluated to be on the order of 15.4% at room temperature, with a small variation <;5.4% in the temperature range of 20-900°C. Moreover, the TmCOB crystals were obtained to possess high piezoelectric coefficientd₂₆ being 7.8 pC/N, 3-4 times that of quartz, and showing a minimal variation of -12.9% over the test temperature range, potential for high temperature piezoelectric applications.

Piezoelectric properties of the monoclinic BIBO single crystals

In this report, the bismuth triborate piezoelectric crystals,α-BiB₃O₆(BIBO), were investigated for potential sensor applications. The dielectric, piezoelectric and electromechanical properties were evaluated by using the impedance method, where the largest piezoelectric charge coefficients were found for d₂₂, being on the order of 40.0pC/N, with corresponding piezoelectric voltage coefficients g₂₂=538×10^-3V·m/N at room temperature (RT). The optimum piezoelectric crystal cuts were further investigated based on the determined electro-elastic constants, where the (XYl)-50°crystal cuts were calculated to possess large shear piezoelectric charge coefficient free of cross-talk, being on the order of d_eff=28.5pC/N, and the Y-oriented crystal cuts were found to possess the largest hydrostatic piezoelectric charge and voltage coefficients, being on the order of d_h=59.2 pm/V and g_h=797×10^-3V·m/N, respectively.