A Sharp Improvement of Sulfate's Birefringence Induced by the Synergistic Effect of Heteroleptic and Dimeric Strategies.

As for tetrahedron-based ultraviolet nonlinear optical crystals, it is so difficult to achieve a sufficient birefringence to satisfy the phase-matching condition. Thereover, it is necessary to greatly increase the polarizability anisotropy of tetrahedra. Meanwhile, the tetrahedra should be arranged as uniformly as possible. Based on these ideas, a new strategy that dimerizes the heteroleptic tetrahedra with heteroleptic atoms as bridges is proposed and implemented, resulting in a new compound, Na2 S3 O6 , which crystallizes in a centrosymmetric monoclinic phase (phase-I) and a non-centrosymmetric orthorhombic one (phase-II). In the phase-I, a large birefringence of 0.103 @ 546 nm comparable to those of many triangle-based crystals is confirmed experimentally, indicating the ability of [S3 O6 ] group in improving the birefringence. Besides, the phase-II exhibits an improved birefringence of 0.056 @ 546 nm and a moderate second harmonic generation response of 1.4 × KH2 PO4 . In particular, the phase-II exhibits a typical phase-matching behavior under the irradiation of 532 nm laser. Moreover, the excellent optical properties of [S3 O6 ] group are further verified by theoretical calculations. These results completely illustrate the validity of the design strategy. Therefore, this work lights a new route for exploring novel ultraviolet nonlinear optical crystals.

Enhanced mechanical quality factor of BiScO3-PbTiO3 piezoelectric ceramics using glass composition.

Compared with pure Pb-based perovskite ferroelectric materials, Bi(Me)O3-PbTiO3 (Me = Sc3+, In3+, Yb3+) have attracted attention due to their remarkable advantage in their Curie temperature. Among them, BiScO3-PbTiO3 piezoelectric ceramic is a potential piezoelectric material in high-temperature applications for its high Curie temperature and excellent piezoelectric coefficient. However, its shortcomings are high dielectric loss and low mechanical quality factor. Herein, we report the improvement of the mechanical quality factor of 0.36BS-0.64PT ceramics through the addition of glass composition (GeO2). There is a small change in the Curie temperature after GeO2 addition. The piezoelectric coefficient d 33 and planar electromechanical coupling factor k p increase first and then decrease, and the mechanical quality factor Q m monotone increases with an increase in GeO2. The 0.36BS-0.64PT + 0.5 mol%GeO2 ceramics have optimal electrical properties with T C of 455 °C, d 33 of 385 pC N-1, k p of 58%, and Q m of 90. In addition, the thermal stability of 0.36BS-0.64PT + xGeO2 and 0.36BS-0.64PT ceramics is almost the same. It was concluded that the mechanical quality factor of BS-PT ceramics can be enhanced by the addition of GeO2 with other properties remaining unchanged.

Phosphogermanate Crystal: A New Ultraviolet-Infrared Nonlinear Optical Crystal with Excellent Optical Performances.

The phase matching ability is a key factor for nonlinear optical crystals to realize coherent output. Herein, a new design strategy combining ultraviolet and infrared functional groups into a ferroelectric was put forward. Thus, a phosphogermanate crystal, KGeOPO4, was designed and studied. It exhibits a wide transparency window (0.22-9.70 µm), a strong second harmonic generation response (5× KH2PO4), a high laser-induced damage threshold (1.61 GW/cm2), and the typical ferroelectricity (coercive field ∼ 9.8 kV/cm and remnant polarization ∼7.6 µC/cm2). In the infrared region, it could realize coherent output by the birefringence phase matching method, while it could generate ultraviolet coherent lights by the quasi-phase matching technique. Therefore, this work designs a promising ultraviolet-infrared nonlinear optical crystal and provides a new perspective for exploring nonlinear optical crystals.

Complete Sets of Material Constants of [001]-Poled 0.72Pb(Mg1/3Nb2/3)O3- 0.28PbTiO3 Single Crystals Using Alternating Current Poling.

Alternating current poling (ACP) is an effective method to improve the piezoelectric performance of relaxor-PbTiO3 (PT) ferroelectric single crystal. 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-PT) single crystals have been used to fabricate piezoelectric transducers for medical imaging. Up to date, there are no reports about the full matrix material constants of PMN-0.28PT single crystals poled by ACP. Here, we report the complete sets of elastic, dielectric, and piezoelectric properties of [001]-poled PMN-0.28PT single crystals by direct current poling (DCP) and ACP through the resonance method. The results show that [001]-poled rhombohedral PMN-0.28PT single crystals exhibit the enhancement of longitudinal and transverse piezoelectric properties ( d33  âˆ¼ 2000 pC/N, d31  âˆ¼ -1010 pC/N) after ACP. Compared with DCP samples ( d33  âˆ¼ 1660 pC/N, d31  âˆ¼ -780 pC/N), the values of d33 and d31 increase 20% and 29%, respectively. While the d15 value decrease from 110 pC/N for DCP sample to 90 pC/N for ACP sample, showing the decrease in transverse shear piezoelectric properties. In addition, the elastic stiffness coefficients c11 , c12 , c13 , the elastic compliance coefficients s11 , s12 , and the dielectric constants ε11 , ε33 have great change compared with DCP and ACP samples. This variation of the property matrices provides a reference for high-performance piezoelectric device design.

Broad bandwidth emission and in situ electric field modulation of photoluminescence in Nd-doped ferroelectric crystals.

The electric field modulation of photoluminescence in ferroelectric-optical materials as a novel in situ, non-damaging and real-time controllable method has drawn much research focus. The broad bandwidth emission of 33 nm and a tuneable luminescence contrast of 28% were achieved in Nd-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Nd:PMNT) tetragonal ferroelectric-optical crystals arising from spontaneous polarization. The study of Nd:PMNT ferroelectric crystals under a cyclic, triangular alternating current voltage wave showed that the change in the photoluminescence intensity subjected to an electric field is mainly related to the 180° domain distribution, rather than the 90° domain. The physical process of electric field tuning luminescence is to control the 180° domain distribution using the external electric field, which thereby effectively tunes the luminescence. This finding restricts the limitation of a specific phase change region, which greatly increases the range of materials used and has guiding significance for research in the electric field modulation of luminescent technology.

Effects of alternating current poling on the dielectric and piezoelectric properties of Pb(In0.5Nb0.5)O3-PbTiO3 crystals with a high Curie temperature.

The alternating current poling (ACP) method has been become more and more popular recently because of its advantages of being low cost, time saving and highly efficient. Few ACP studies have focused on relaxor-PT crystals with a high coercive field and high Curie temperature or the effects of ACP on intrinsic and extrinsic contributions. The effects of the electric field, frequency, and number of cycles of ACP on the piezoelectric and dielectric properties of 〈001〉-oriented Pb(In0.5Nb0.5)O3-PbTiO3 ferroelectric crystals were studied. The dielectric permittivity ε 33 T /ε 0 and piezoelectric coefficient d 33 of an ACP sample are 3070 and 1400 pC N-1, respectively, which are 14% and 18% larger than those of a DCP sample. Rayleigh analysis reveals that both intrinsic and extrinsic contributions are enhanced after ACP. The poling electric field, frequency and cycle number can influence the intrinsic and extrinsic contributions. The intrinsic contribution is significantly affected by the poling electric field, and cycle number, but it is not very sensitive to frequency, while the poling electric field, frequency and cycle number are very important for the extrinsic contribution. This work demonstrates that the uniform domain patterns are a critical factor for the enhancement of the piezoelectric properties.

Zn3B7O13Cl: A New Deep-Ultraviolet Transparency Nonlinear Optical Crystal with Boracite Structure.

Nonlinear optical crystals play important roles in modern laser science and technology. However, the design and growth of new nonlinear optical (NLO) materials is still a challenging issue for researchers. Due to the excellent performance of Mg3B7O13Cl crystal, we paid attention to the optimization of its structure, in order to find new NLO materials with favorable properties. Here, Zn3B7O13Cl crystals were obtained by a high-temperature solution method. Its structure was determined to be the trigonal symmetry with a polar space group of R3c, which is more highly symmetric than that of Mg3B7O13Cl (Pca21). The experimental and theoretical investigations demonstrated that the title compound exhibits a short absorption cutoff (band gap ∼6.53 eV), moderate SHG responses (2.2 times that of KDP at 1064 nm), and the improved birefringence, which results from the large distortion and anisotropy of borate groups and zinc polyhedrons. Therefore, the structural modification of Mg3B7O13Cl by zinc cations achieves a balance between the deep-ultraviolet transparency, the nonlinear optical effect, and the moderate birefringence, which is very significant for the design of practical NLO materials.

Ca2B5O9Cl and Sr2B5O9Cl: Nonlinear Optical Crystals with Deep-Ultraviolet Transparency Windows.

M2B5O9X is a prominent family with excellent nonlinear optical (NLO) responses, just as the Pb2B5O9I crystal with a large second harmonic generation (SHG) of 13.5 times that of KH2PO4. However, most of these compounds are limited to ultraviolet and visible regions because of their long absorption edge (small band gap). Here, we report two members of this family, which change the situation. Using a high-temperature solution method, we obtain Ca2B5O9Cl and Sr2B5O9Cl crystals, which exhibit a deep-ultraviolet (DUV) absorption edge of 170 nm (band gap ≈ 7.29 eV). It is an important breakthrough in the DUV transparency of the M2B5O9X family. Furthermore, Ca2B5O9Cl crystals display a phase-matching SHG response under a 1064 nm laser, which is further confirmed by the balance between the suitable birefringence and the small dispersion of refractive indexes in the wavelength range of 1064-532 nm. Therefore, they are promising DUV transparency windows and NLO candidates.