Chengqian Zhang

MgTeMoO6: A neutral layered material showing strong second-harmonic generation

A noncentrosymmetric (NCS) compound, MgTeMoO6, has been synthesized using the high temperature solution method with TeO2–MoO3 mixture as a flux. MgTeMoO6 crystalizes in the orthorhombic space group P21212 (No. 18) with cell parameters a = 5.03780(10) A, b = 5.26910(10) A, c = 8.8985(2) A, and Z = 2. The compound exhibits a novel neutral layered structure consisting of asymmetric MgO6 octahedra, TeO4 polyhedra and MoO4 tetrahedra. Thermal stability measurements revealed an incongruent melting point of 682.35 °C. The crystal exhibits a very broad transmission range from 360 nm to 5.2 μm. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicates that the crystal exhibits a strong SHG efficiency of ∼1.5 × KTiOPO4. Additional SHG measurements indicate the material is type-I phase-matchable. Furthermore, calculations on the local dipole moment indicates that the strong SHG response of MgTeMoO6 is mainly caused by the three types of NLO-active units (TeO4, MoO4 and MgO6).

Bulk crystal growth and characterization of a new polar polymorph of BaTeMo2O9: α-BaTeMo2O9

Bulk single crystals of α-BaTeMo2O9 with dimensions up to 51 × 30 × 20 mm3 were grown successfully by a top-seeded solution growth (TSSG) method using TeO2-MoO3 mixture as a flux. High-resolution X-ray diffraction measurement on the (400)-faced plate indicates that the full-width at half-maximum (FWHM) of the rocking curve is 16.55′′. The as-grown crystal exhibits {010}, {002}, {110}, {111} and {201} facets, which are in good accordance with the predicted growth morphology based upon the Bravais-Friedel and Donnay-Harker (BFDH) method. In addition, thermal properties including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated as a function of temperature. The average linear thermal expansion coefficients along the a-, b-, and c-axis from 30 °C to 500 °C were measured to be αa = 9.10 × 10−6 K−1, αb = 19.58 × 10−6 K−1 and αc = 11.94 × 10−6 K−1, respectively. The specific heat was measured to be 0.433–0.566 J (g K)−1 over the temperature range of 30–540 °C. The thermal conductivity along the a-axis is larger than those along other directions (κa>κb> κc). The transmission spectra and refractive indices were also measured. The α-BaTeMo2O9 crystal exhibits a wide transmission window ranging from 380 nm to 5530 nm. The large birefringence of α-BaTeMo2O9 (Δn = 0.305 for light at 404.7 nm) indicates that it is not only Type I and II phase-matchable, but also a very promising candidate for optical devices.

Synthesis, crystal growth, and characterization of the orthorhombic BaTeW2O9: a new polymorph of BaTeW2O9

A new polymorph of BaTeW2O9 with space group Pnma was identified during the exploration of the BaO-WO3–TeO2 system. Single-crystal X-ray diffraction measurements show that the material exhibits a 3D tunnel structure consisting of W–O6 octahedra connected with Te–O3 tetrahedra. Bulk single crystals of orthorhombic BaTeW2O9 with dimensions of 24 mm × 22 mm × 15 mm were grown by a top-seeded solution growth (TSSG) method using TeO2 as flux. Theoretical morphology of the crystal was obtained using the Bravais–Friedel and Donnay–Harker methods for comparison. The crystal shows a high transmittance from 360 nm to 5 μm as well as large birefringence (with Δn = 0.247 at 404.7 nm). The Raman spectrum shows that there is a Raman shift with high intensity and narrow peak width at 910.93 cm−1. TGA and DSC analysis indicate that the material melts incongruently at 783 °C. The thermal conductivity of the crystal was measured to be 1.23, 2.61 and 0.95 W m−1 K−1 at 50 °C along the a-, b- and c-axes, respectively.

Second order nonlinear optical properties of Cs 2 TeW 3 O 12 single crystal

We report the linear and nonlinear optical (NLO) properties of a polar crystal Cs2TeW3O12 (CTW). The second-order NLO coefficients were determined by Maker Fringe (MF) techniques for the first time. CTW belong to hexagonal system with point group P63, the two independent NLO coefficients of d32 and d33 were determined to be 6.2 and 4.3 pm/V, respectively. CTW can realize phase-matching (PM) and in the direction of θ = 39.6° the effective NLO coefficient is 4.0 pm/V at 1064 nm. To illustrate the good NLO properties of CTW, the distortions of polyhedron structures were also discussed in detail.

Characterization and optimization of the growth conditions of a novel Cs2TeW3O12 piezoelectric crystal

In this study, Cs2TeW3O12 (CTW) single crystals were grown successfully through a top-seeded solution growth (TSSG) method using TeO2 as a self-flux. We identified a complete set of growth process parameters suitable for facilitating the growth of a high-quality CTW crystal. The results indicate that, in the same thermal field and with an appropriate flux ratio, a smaller cooling rate of the melt facilitates the smooth growth of high-quality CTW single crystals. The melt-viscosity versus temperature curves for different flux ratios were measured, and their effects on the crystal quality were discussed. In addition, the morphology of the crystal can be controlled by adjusting the rotation speed and the orientation of the seed. To investigate piezoelectric performance, complete sets of dielectric, elastic, and piezoelectric coefficients of CTW crystals were measured using both resonance and impedance analysis. The piezoelectric coefficients d33 and d15 reached 19.1 pC N−1 and 25.9 pC N−1, respectively. The electromechanical coupling coefficient, k33, was 37.7%, slightly higher than that of Cs2TeMo3O12 (CTM). Furthermore, the extent of dipole moment and polyhedron distortion of the CTW crystal were analysed in detail, and the relationship between the crystal structure and the piezoelectric properties was also discussed.