Shiji Fan

Thermal and Nonlinear Optical Properties of Ca4YO(BO3)3

Ca 4 YO(BO 3 ) 3 (YCOB) crystals have been grown using the vertical Bridgman method. The thermal properties of YCOB were measured for the first time to our knowledge. The specific heat is 729.7 J/kg K at 373K. The average thermal expansion coefficients along the a, b and c axes are 9.9×10 -6 /K, 8.2×10 -6 /K and 12.8×10 -6 /K. respectively, in the temperature range of 293-1173K. The thermal conductivities along the a, b and c axes are 1.83W/mK, 1.72W/mK and 2.17W/mK at 373K. The anisotropy in the measured thermal conductivities of YCOB is consistent with the experimental results of the thermal expansion. The SHG of a Nd: YAG laser was compared with that of a KDP crystal. The effective nonlinear coefficients (d eff ) of YCOB in type I phase matching directions of (θ, Φ)=(66.3°, 143.5°) and (65.9°, 36.5°) were estimated to be 1.45pm/V and 0.91pm/V, respectively. The bulk damage threshold was observed as 85GW/cm 2 for single pulse of a Nd:YAG laser with 10ns pulse duration.

Seeded Growth of Relaxor Ferroelectric Single Crystals Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 by the Vertical Bridgman Method

Relaxor ferroelectric single crystals Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT91/9) with a dimension of 30 mm in diameter and 25 mm in length have been grown by the modified vertical Bridgman method using PbO as the flux. Initially, seed crystals were obtained by cooling high-temperature solutions at the rate of 0.8–2°C/h. PZNT91/9 crystals were grown in a platinum crucible with a seed well of 10 mm×60 mm from different solutions. It is difficult to grow perovskite PZNT crystals from 91 mol% Pb(Zn1/3Nb2/3)O3–9 mol% PbTiO3 melts with a surplus of PbO due to the competition of the pyrochlore phase. Additionally, a Pt crucible is prone to severe erosion by PbO at high growth temperatures. The optimum flux concentrations were found to be 45–55 mol% and the growth rate was 0.3–0.6 mm/h. Twelve pieces of PZNT wafers without any PbO striation were obtained. The dielectric properties of the grown crystals were determined.

Properties, production and application of new piezoelectric crystal lithium tetraborate Li/sub 2/B/sub 4/O/sub 7/

The piezoelectric, elastic, dielectric, thermal, optical, mechanical, chemical, surface acoustic wave (SAW) and bulk acoustic wave (BAW) coupling, and propagation properties of new piezoelectric-crystal lithium tetraborate Li/sub 2/B/sub 4/O/sub 7/ (LBO) are reviewed. The growth and production of LBO crystal by the modified Bridgman (BR) technique (Fans process) and its application to SAW and BAW devices are also discussed. Attention is also given to such features of LBO growth as the critical requirement of stoichiometric purity for raw material, very low crystal growth rate, a convex or plane solid-liquid interface in the growth, a suitable procedure of self-annealing, and the practicality of the BR technique for commercialization of LBO material with a large diameter of 82 mm and high quality.<<ETX>>

Bridgman growth and characterization of nonlinear optical single crystals Ca4GdO(BO3)3

Nonlinear optical single crystals Ca 4 Gdo(BO 3 ) 3 (GdCOB) have been grown by the vertical Bridgman method. Bubble-free, twin-free and crack-free GdCOB single crystals 25 mm in diameter and 65 mm in length were obtained. The average thermal expansion coefficients along a-, b- and c-axes from 293 to 1273 K are 10.35 × 10 - 6 K - 1 , 7.78 ×10 - 6 K - 1 and 13.10 ×10 - 6 K - 1 , respectively. The bulk damage threshold is 130 GW cm - 2 for a single pulse of a mode-locked Nd:YAG laser with 35 ps pulse duration. The effective nonlinear coefficient (d e f f ) in the phase matching directions of (θ, Φ) = (66.8°, 132.6°) is 1.51 pm V - 1 .

Bridgman growth of lead potassium niobate crystals

Lead potassium niobate Pb 2 KNb 5 O 15 (PKN) crystals with tetragonal tungsten bronze (TTB) structure have been grown by the modified Bridgman (BR) method. Nearly sealed Pt crucibles and small temperature gradients in the Bridgman furnace can limit volatilization of PbO and cracking of as-grown PKN crystals. Transparent PKN crystals of 1 inch diameter by ∼ 2 inch length with brownish color have been grown successfully at a crucible lowering rate < 0.5 mm/h and a temperature gradient of 10-15°C/cm across the solid-liquid interface. Coupling between twins and growth directions of the crystal is also discussed.

Ferroelectric potassium lithium niobate crystals grown by the vertical Bridgman method

Ferroelectric potassium lithium niobate (KLN) single crystals are very promising candidates for direct second harmonic generation of semiconductor diode lasers. In this paper, crack-free KLN crystals up to 10 mm in diameter by 50 mm in length were grown by the modified vertical Bridgman method from potassium and lithium enriched solutions. Prior to growth, KLN powder was prepared by sintering the mixture of K2CO3, Li2CO3 and Nb2O5 at 850°C for 8 h. Two temperature zones were designed in the Bridgman furnace to prevent crystals cracking. The growth rate is less than 0.25 mm h−1 and the temperature gradient in the solid–liquid interface is about 20°C cm−1. The transparent KLN crystal has a very good transmittance in the 420–800 nm region with an absorption edge at 378 nm. Dielectric constant of e33 and e11 at room temperature are 127 and 376, respectively. Curie temperature of the crystal is about 380°C.

Mechanical properties anisotropy of PZNT93/7 single crystal

The mechanical properties of 93%Pb(Zn1/3Nb2/3)O3–7%PbTiO3 (PZNT93/7) single crystal were evaluated by microindentation and nanoindentation techniques. The (1 1 1) facet of the crystal exhibited excellent combination mechanical properties (Vickers microhardness Hv, fracture toughness Kc and elastic modulus Er) than those of (0 0 1) facet. The Hv on (1 1 1) and (0 0 1) facets were 3.71 GPa and 3.00 GPa, respectively. In-plane fracture toughness anisotropy was observed on both the (1 1 1) and (0 0 1) facets, the Kc value was low in the direction parallel to the domain wall but large in the direction perpendicular to it. The Er of (0 0 1) and (1 1 1) facets was independent of the load, Er(1 1 1) was measured to be about 130 GPa and Er(0 0 1) was about 110 GPa. The above results implied that (0 0 1) PZNT crystals would face a more severe challenge in device application due to their weaker combination mechanical properties but outstanding piezoelectric properties than those of (1 1 1) PZNT crystals.

Phase equilibria in the pseudo-binary systems LiF–CaAlF5 and LiF–SrAlF5

Abstract The phase equilibria in pseudo-binary systems LiF–CaAlF 5 and LiF–SrAlF 5 have been studied by means of differential thermal analysis and X-ray diffraction. The two analogous phase diagrams show that the compounds LiCaAlF 6 and LiSrAlF 6 melt congruently with the composition of LiF:CaAlF 5 =1:1 and LiF:SrAlF 5 =1:1 at 814°C and 765°C, respectively. There are two eutectic relationships in the system LiF–CaAlF 5 , one between the compounds LiF and LiCaAlF 6 with the eutectic temperature of 705°C, the other between LiCaAlF 6 and CaAlF 5 with the eutectic temperature of 781°C. The system LiF–SrAlF 5 also has two eutectic relationships at the left or right side of the compound LiSrAlF 6 with the eutectic temperatures of 673°C and 705°C, respectively. Using the feed materials with the stoichiometry compositions, large-size fluoride laser crystals Cr 3+ :LiCaAlF 6 and Cr 3+ :LiSrAlF 6 with high quality have been grown successfully by the vertical Bridgman method.

Growth and characterization of potassium lithium niobate crystals

Tetragonal tungsten-bronze potassium lithium niobate crystals (KLN) were grown by vertical Bridgman technique. Transparent KLN crystals with 10 mm in diameter and 25 to 45 mm in length were obtained. Crystallization behavior from different KLN melts was studied. It was found that KLN crystals will stop growing after the melt composition changes to some critical value and other phases, such as KNbO3, LiNbO3 and Li3NbO4, crystallize at the same time. Inhomogeneity and cleavage of as-grown KLN crystals were discussed.

A typical defect in the Bridgman-grown LBO crystals

A typical macro-defect, a veil-like layer in the Bridgman-grown <110> LBO crystals, was discovered. The veil-like layer seems to be a semi-transparent veil which covers the whole or partial cross section in the growth direction. The mechanism for formation of the veil-like layer defect has been explored by determining morphology and distribution of the defect and analyzing the relationship between the crystal growth conditions and the defect. The veil-like layer defect is microcrack in which there is decomposition on surface of the crack or deposition of vapor of LBO melt in as-grown LBO crystals.