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The thermal properties of orthorhombic AgGaGeS4 and chalcopyrite AgGaS2 crystals, including thermal expansion, specific heat, and thermal conductivity, have been investigated. For the AgGaS2 crysta...

AgGaGeS4 is a new quaternary chalcogenide nonlinear optical crystal in application to converting a 1.064 μm Nd:YAG laser to 4–11 μm mid-IR output. It has been clearly demonstrated a high laser damage threshold, 50 MW cm−2 at 1.064 μm, which makes it a promising material for high-power and sustained laser frequency conversion. However, the preparation of the AgGaGeS4 single crystal has been perplexed by the complex multiple chemical reactions, high vapor pressure and large undercooling degree. In this work, a unique cooling process is used to modify the vapor transport with mechanical oscillation method for higher quality polycrystal. Besides, diverse ways have respectively addressed the pivotal issues of crystal growth process by the Bridgman method, such as the degree of supercooling, growth rate and control of decomposition at high temperature. Eventually, we have obtained the AgGaGeS4 crystal and the maximum size is Φ30 mm × 50 mm. In addition, the non-polarization Raman spectra were recorded at room temperature with a 532 nm laser beam excitation source. The main vibration frequencies present around 107, 323 and 355 cm−1, and the relationship between the structure and lattice vibrational properties is also discussed and analyzed in detail. The crystal performs a good homogeneity and high transparency in the 0.5–11.5 μm spectral range, especially the absorption coefficient of annealed AgGaGeS4 wafer that ranges from 0.01 cm−1 to 0.05 cm−1 in 0.9–10 μm after annealing, which illustrate it suitable for further optical experiments and the comprehensive applications. Besides, the band gap changes from 2.787 eV to 2.805 eV after annealing. At last, the surface damage threshold is about 103 MW·cm−2 which is two times more than report, and the body damage threshold is about 132 MW·cm−2.

AgGaGeS4 is a new promising nonlinear-optical crystal for frequency-shifting a 1.064 μm laser into mid-IR. This quaternary compound single crystal has been successfully grown by a modified vertical...

AgGaGe nS2( n+1) crystal is a series of quaternary nonlinear optical materials for mid-IR laser applications of converting a 1.064 μm pump signal (Nd:YAG laser) to 4-11 μm laser output, but only AgGaGeS4 has attracted the most attention, remaining the other promising AgGaGe nS2( n+1) crystal whose physicochemical properties can be modulated by n value. In this work, AgGaGe nS2( n+1) ( n = 2, 3, 4, and 5) polycrystals are synthesized by vapor transport and mechanical oscillation method with different cooling processes. High-resolution X-ray diffraction analysis and refinement have revealed that all the four compounds are crystallized in the noncentrosymmetric orthorhombic space group Fdd2, resulting in the excellent nonlinear optical property, and the distortion of tetrahedron with the variation of n value causes the discrepancy of physicochemical property. Besides, using the modified Bridgman method, AgGaGe nS2( n+1) single crystals with 15 mm diameter and 20-40 mm length have been grown. We have discussed the structure and composition of AgGaGe nS2( n+1) by XPS spectra and analyzed the three kinds of vibration modes of tetrahedral clusters by the Raman spectra. The Hall measurement indicates that the AgGaGe nS2( n+1) single crystals are p-type semiconductor, and the carrier concentration decreases with the increasing n value. All the transmittances of as-grown AgGaGe nS2( n+1) samples exceeds 60% in the transparent range, especially the transmittance of AgGaGe2S6, is up to 70% at 1064 nm, and the band gap of as-grown crystal increases from 2.85 eV for AgGaGe2S6 to 2.92 eV for AgGaGe5S12. After a thermal annealing treatment, the absorptions at 2.9, 4, and 10 μm have been eliminated, and the band gap changed into the range of 2.89-2.96 eV.

Free-standing BiI3 single-crystal flakes with a rhombohedral appearance and 10–100 µm in thickness were prepared by using physical vapor transport method. The (00l) (l = 3, 6, 9, 12) planes of the as-grown crystal present a distribution of layered structure and approximatively atomically smooth surface with 1.3–1.7 nm step height and roughness average 0.38–0.65 nm. Both planar and coplanar electrode configuration devices for X-ray detection were fabricated with the as-grown BiI3 single crystals and the dark resistivity 5.8–6.4 × 1011 Ω cm and 1.2–1.8 × 1011 Ω cm at room temperature were obtained, respectively. A low dark current or high resistivity for planar device is on account of carrier scattering from the I–Bi–I interlayer van der Waals bonding interface. A high net photocurrent and good sensitivity 1.22–1.36 × 104 µC/Gyair/cm2 under X-ray excitation were also obtained with planar device owing to the uniform electric field distribution and high charge collection efficiency.

Chalcopyrite ZnGeP2 single crystal with sufficient size and quality was grown by modified vertical Bridgman method. The thermal expansion coefficients along a-axis and c-axis, αa and αc, were evaluated from the results of thermal dilatometer tests carried out in the range of 300–600 K. It is found that both αa and αc achieve positive values and αa is always larger than αc in the whole range indicating that the thermal expansion of the crystal exhibits anisotropic behavior. We selected the sample of c-axis and measured its thermal conductivity and molar specific heat. On this basis, the Gruneisen parameters of c-axis at different temperatures were calculated. Using these Gruneisen parameters, the lattice thermal conductivities have been deduced by one correction formula and we found that they are very close to the experimental results.

Cd1−xZnxTe (CZT) films were deposited on ITO substrates at different substrate temperature by repeatedly RF magnetron sputtering with a Cd0.9Zn0.1Te target. The effect of substrate temperature on physical properties of CZT films were systematically investigated. The morphology of CZT films were characterized by atomic force and scanning electron microscopes. The grain size increased and grain boundaries decreased with substrates temperature increasing. XRD studies revealed that as-grown CZT films were polycrystalline with (111) preferential orientation and the crystallization quality was improved with the increase of substrate temperature. Optical analysis of CZT films showed the band gap decreased with the substrate temperature increasing. A1 and A2 detectors were fabricated based on the CZT films deposited at 300 and 400 °C, respectively. The electrical and X-ray response properties at room temperature of two detectors were investigated. The dark resistivity is 1.49 × 108 and 4.26 × 108 Ω cm for A1 and A2 detectors, respectively. The X-ray sensitivity of CZT films deposited at 400 °C was higher than that of CZT films deposited at 300 °C.

Thermal expansion coefficients of AgGa1−xInxSe2 (x = 0.2, 0.3, 0.4) single crystals have been measured in the range from 323 K to 823 K. The values of αa are positive and increase with temperature whereas the values of αc are negative and their absolute magnitudes increase with the increasing temperature for different x. With the increase of x, thermal expansion coefficients αa and αc both decrease numerically. The mean linear thermal expansion coefficient αL and the anisotropy of thermal expansion αη have been calculated, and they are also decreasing numerically with the increasing x. The slope of the straight line α hkl versus co s 2 ϕ decreases as x increases at 473 K and 773 K, respectively. According to the variation of thermal expansion coefficients, the relationship between the thermal expansion coefficient, bond length, and melting point of AgGa1−xInxSe2 satisfies the equation α L = 0.021 T m − B ( d − d 0 ) 3 . In addition, the mechanism of thermal expansion variation has been discussed in terms of crystal structure, bond lengths, and thermal vibration of bonds in AgGa1−xInxSe2 single crystals.

In this work, laser-induced surface recrystallization process was developed to improve the surface properties and device performance of the polycrystalline PbI2 thick films prepared by using close space vapor deposition method. A continuous polycrystalline PbI2 recrystallized layer with a better mechanical strength and reflectivity improved from 2% to 4%–6% was obtained by this recrystallization process for the films with mechanical pretreatment. Other polytypes is absent in the recrystallized layer with the 2H-polytype remaining before and after treatment and obtaining improved electrical and X-ray photoelectric response performance. The pretreatment such as mechanical cutting/polishing and hydrogenation is necessary to lower the non-wetting crystallization behavior during the recrystallization process due to the rough surface state and oxygen contamination.

CdSiP2 is the only crystal that can offer Non-critical Phase Matching (NCPM) for a 1064 nm pumped optical parametric oscillation (OPO) with idler output in the 6 μm range. In this paper, a large, crack-free CdSiP2 single crystal measuring 18 mm in diameter and 65 mm in length was successfully grown by the Vertical Bridgman method (MVB) with an explosion-proof quartz ampoule. The results of lattice parameters, element composition and IR transmittance of the as-grown crystal characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS) and Fourier transformation infrared spectrometer (FTIR) showed the as grown crystal crystallized well and the absorption coefficients at 4878 cm−1 and 2500 cm−1 were 0.14 cm−1 and 0.06 cm−1. Moreover, a new etchant composed of Br2, HCl, HNO3, CH3OH and H2O (1:800:800:400:400 in volume ratio) was prepared and the dislocation etch pits on oriented faces of as-grown CdSiP2 crystal were observed for the first time. It is found the etch pits are in rectangular structure on the (1 0 1) face, but in trigonal pyramid structure on (3 1 2) face. According to the quantities of the etch pits, the average densities of dislocation were evaluated to be 2.28 × 105/cm2 and 1.4 × 105/cm2, respectively.

The effects of temperature gradients and crucible materials on ZnGeP2 single crystal, grown by vertical Bridgman method, were studied. Growth were carried out in quartz crucible, quartz crucible with carbon film coated on the inner wall, and PBN crucible respectively. X-ray diffraction (XRD), X-ray fluorescence (XRF) and Fourier transform infrared spectrophotometry (FTIR) were employed to characterize the quality of grown crystals. By annealing in ZnGeP2 powder, its optical properties were found to be improved. A ZnGeP2 optical parametric oscillator (ZGP-OPO) sample was fabricated from the annealed crystal. Laser experiments were carried out on ZGP-OPO by 2.1 µm, 7 kHz laser to obtain tuning laser in the range of 3–5 µm.

Cr-doped CdGeAs 2 polycrystal was synthesized by a single-temperature region combined with mechanical and temperature oscillation method, and Cr-doped CdGeAs 2 single crystal with Φ17 mm × 30 mm was grown by the improved Bridgman method. The crystal structure, electrical properties and doping content of Cr-doped CdGeAs 2 were characterized by high-resolution XRD, Hall-effect and ICP, respectively. In the XPS measurement, the high-resolution scanning spectra of the Cr-doped CdGeAs 2 crystals were obtained for the first time, and the binding energies of Cr 2p 3/2 are 575.44 eV and 576.50 eV, and the binding energies of Cr2p 1/2 are 583.06 eV and 585.14 eV by peak separation and fitting. Finally, FTIR was used to characterize the infrared properties of Cd-doped CdGeAs 2 crystals. The results show that the transmittance near 5.5 μm increases with a small amount of doping compared to undoped crystal, and reaches a maximum 42% when the Cr content is 0.057%. When the Cr content increases to 0.158%, the transmittance decreases slightly, and while the content reaches 0.324%, the transmittance of the whole wavelengths decreases sharply. Appropriate amount of Cr can reduce the absorption of CdGeAs 2 near 5.5 μm, improve its infrared transmittance and broaden its applications.

X-ray photoelectron spectroscopy (XPS) was proposed as suitable method to study the low content of impurity phases on ZnGeP 2 (ZGP) single crystals which are excellent materials in non-linear infrared fields. Besides it, X-ray diffraction (XRD) and Energy Dispersive Spectrometer (EDS) tests were carried out to characterize the components homogeneity of the crystal. It is found that impurity phases Zn 3 P 2 and ZnP 2 , which are undetectable by X-ray diffraction (XRD) method due to low content, results in the heterogeneity of components and phases of ZGP single crystal. Meanwhile, Oxides of P 2 O 5 and GeO 2 were found to exist on the surface of the crystal.

Single-phase AgGaGeS4 polycrystalline materials were synthesized directly from the constituent elements by vapor transporting and mechanical oscillation method. The problem of explosions was solved by careful control of the heating and cooling cycle and adopting the two-zone rocking furnace with specially designed temperature profile. The mechanical and temperature oscillations, as well as gradient cooling, were introduced in the synthesis process. The X-ray diffraction (XRD) analysis and Energy Dispersive Spectrometer (EDS) micro analysis indicated that the synthesized compound is a single-phase AgGaGeS4 polycrystalline material.

The exfoliated CdZnTe (CZT) films were grown on quartz substrates by closed tube physical vapor transport method based on stress mismatch mechanism. The structure and morphology of the exfoliated CZT thick films were characterized by X-ray diffraction and scanning electron microscope. The as-grown CZT films are polycrystalline with (111) preferential orientation and exhibit a dense pyramid surface structure and a thickness of more than 600 μm. The coplanar and planar X-ray detectors were fabricated based on the exfoliated CZT film. The discrepant dark resistivity is 3.17 × 109 and 5.14 × 1010 Ω cm with regard to the coplanar and planar structure detector, respectively. The planar structure detector exhibits higher quantum efficiency at low doses X-ray radiation.

The performances of second harmonic generation (SHG) and optical parametric oscillator (OPO) in CdGeAs2 crystal are strongly influenced by surface quality. In this paper, the surfaces of samples were treated by mechanical polishing (MP), chemical polishing (CP), chemical–mechanical polishing (CMP) and CP following CMP closely (CMP + CP). Then, the surface state was characterized by optical microscopy (OM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM measurements show that an ultra-smooth surface is achieved after CMP + CP treatment and the roughness value is 0.98 nm. Meanwhile, the roughness of the surfaces treated by MP, CP and CMP are 4.53, 2.83 and 1.38 nm, respectively. By XRD rocking curves, the diffraction peak which belongs to the wafer treated by CMP + CP is the highest in intensity and best symmetrical in shape. XPS analysis indicates that Ge4+ proportions of GeO2 in total Ge content of CdGeAs2 wafers’ surface after MP, CP, CMP and CMP + CP treatment are 27.6%, 42.8%, 6.1% and 30.3%, respectively.

Thermal expansion coefficients measurements of AgGa 0.7 In 0.3 Se 2 with the direction of c- and a- axis are made in the temperature range between 300 and 900 K. It is obviously that AgGa 0.7 In 0.3 Se 2 is with a reverse thermal expansion behavior along the c -axis, and variation of directional coefficient at different temperatures as a function of cos2φ has been discussed in this work. It’s found that the crystal would expand with increasing temperature if the angle between the direction [ hkl ] and the c-axis is greater than 42.71°. In addition, Gruneisen parameters at different temperatures have been calculated and also exhibit anisotropic behavior ( γ a > γ c ). At last, by a modified formula, variation of lattice thermal conductivity with temperature have been deduced. And the calculation value at room temperature is a little larger than the measurement value of thermal conductivity with [100] direction at room temperature which is found to be 0.751 W/m K.

AgGaGeS

AgGaGe

The optical-phonon spectra of CdGeAs2 were investigated by low temperature polarized Raman scattering. According to vibrational modes of ZnS-type materials and selection rules of Raman scattering, all Raman active vibrational modes in the Brillouin-zone (BZ) center of CdGeAs2 predicted from group-theory arguments were identified and artificially grouped in three energy bands, including 45–94, 158–215 and around 260 cm−1. Based on the Lyddane-Sachs-Teller (LST) relation and measured refractive indices, the low-frequency dielectric constant e(0) is estimated to be 15.04 and shows good agreement with the previous tests and predictions.

Chalcopyrite of CdGeAs 2 single crystal was grown by a modified vertical Bridgman method with sufficient size and quality, and its optical, electrical and thermodynamic properties are characterized. The transmission is recorded in the 2.3–18 μm range, and the band-gap at room temperature is at 0.56 eV. Non-ideal transparency near 5.5 μm which limited its application severely exists in the front of the crystal. The crystal is p type at room temperature with hole concentrations varying from 10 14 to 10 16 cm −3 . From the results of X-ray diffraction measurements carried out over the range 25–450 °C and thermal dilatometer tests, the thermal expansion coefficients are evaluated. And on this basis the Gruneisen parameters at different temperatures are evaluated and also exhibit anisotropic behavior ( γ a > γ c ). It is found that γ a , γ c , and γ V have some difference between these two kinds of test methods. Using these Gruneisen parameters, lattice thermal conductivities have been deduced by two correction formulas. Meanwhile, specific heat capacity and thermal conductivity of [204] have been obtained as a function of temperature by experiment.

A high-quality ZnGeP2 (ZGP) single crystal with large size of Φ30 mm × 80 mm was grown by a modified vertical Bridgman method. ZGP wafers were annealed with ZGP polycrystalline powder for 300 h at 550, 600 and 650 °C, respectively. The as-grown and annealed crystals were characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), IR microscope and energy-dispersive spectroscopy (EDS). Results show that the quality of all wafers is improved evidently after annealing and the optimum annealing temperature obtained is 600 °C. The IR transmittance of the wafer measured by FTIR is up to 56.78 % at wavelength of 2.0 μm nearby and exceeds 59.00 % in the wavelength range of 3.0–8.0 μm. The deviations from stoichiometry decrease, and the homogeneity of the crystal is also improved after annealing. In this paper, scanning infrared map was proposed as a new nondestructive method to evaluate optical quality and homogeneity of crystal through comparing the IR transmittance with the three-dimensional IR spectral contour map.

As a promising material for second harmonic generation (SHG) and optical parametric oscillator (OPO), CdGeAs 2 single crystals are difficult to reproducibly grow with low loss optical, particularly in the region of 5.5 μm. In addition, a correlation between processing conditions and absorption has attracted various researchers to focus on this problem. This paper describes a series of etching experiments and Hall measurements which were undertaken to see if there might be a relationship between dislocation density, carrier concentration and optical absorption. In this study, a single crystal was grown by the modified Vertical Bridgman method. The spontaneous nucleation growth direction has been determined as [102]. Etch pit densities (EPD) about 10 5 cm −2 were observed at the edges of the boules, whereas etch pits were almost not found in the center. The distribution of dislocation along the radial direction affected optical homogeneity, and the high EPD caused the low transmittance. Meanwhile, the samples are p type at room temperature with hole concentrations varying from 10 14 to 10 16 cm −3 . A linear correlation between absorption at 5.5 μm and hole concentration is established. The results of these experiments are very useful for improving radial and axial optical uniformity of the crystal grown by modified Vertical Bridgman method.

In present work, thermal properties of silver thiogallate (AgGaS 2 ) crystal were investigated by means of differential scanning calorimetry (DSC) measurements performed at different heating and cooling rates. The DSC results confirmed that the melting point was 1249 K with a slight change around 5 K and that the nucleation temperature varied from 1183 K to 1218 K. The supercooling temperature was evaluated in the range 37.69 K to 62.46 K which was considered to be harmful for the single nucleus formation at the beginning of crystal growth. The activation energy E and the pre-exponential factor A were also calculated using different isoconversional methods, namely Kissinger–Akahira–Sunose (KAS) method and Flynn–Wall–Ozawa (FWO) method, and the results showed good agreement with each other. According to the results of DSC, a larger temperature gradient up to 30 K/cm was utilized to suppress the formation and growth of multi nuclei and a rapid cooling rate 25 K/min was applied to minimize the second-phase precipitates during the process of crystal growth. Finally, an integral and transparent AgGaS 2 single crystal with diameter of 22 mm and the length of 55 mm was obtained.

The elastic, electronic and optical properties of e-GaSe layered semiconductor have been studied from the first principles with the local density approximation (LDA). The optimized structure of GaSe has been found to be in good agreement with the experimental results. The mechanical stability of e-GaSe is confirmed by calculations of the elastic constants. The calculated band structure shows that the crystal has a direct band gap of 0.816 eV. Furthermore, the linear photon-energy-dependent dielectric functions and some optical constants such as refractive index, extinction, reflectivity and absorption coefficients have been calculated.

We performed the first-principles calculations on the elastic and thermal properties for chalcopyrite ZnSnX2 (X = P, As, Sb), employing the ultrasoft pseudo-potentials and generalized gradient approximation (GGA) under the frame of density functional theory. The equilibrium structural lattice constants are in good agreement with reported data. The elastic characteristics were evaluated under high-pressure condition (0–20 GPa), such as the elastic constants, bulk modulus, shear modulus, Poisson’s ratio, Zener anisotropy and compressibility index. Combining with quasi-harmonic Debye model, the thermal properties were confirmed at different temperatures (0–1200 K) and pressures (0–20 GPa), including the heat capacity, thermal expansion, Debye temperature, entropy, and Grüneisen parameter. Based on the semi-empirical relation, the hardness of materials was determined at various temperatures and pressures. Finally, the phonon spectrum curves and vibration frequencies of phonon were evaluated to confirm the thermodynamic stability of ZnSnX2. The Raman scattering spectrum and infrared absorption spectrum were simulated for chalcopyrite ZnSnX2.

By the method of descending crucible with rotation, crack-free CdGeAs2 single crystals of Φ15 mm × 50 mm were grown in a furnace with three independent heating zones after optimizing the temperature field, and the descending and rotational speed to meet the need of CdGeAs2 crystal growth. The properties of as-grown crystal were characterized by a variety of techniques. The results of X-ray diffraction (XRD) show that there are two cleavage faces, which are (110) and (101). The peaks are in high intensity and good symmetry, which demonstrates that the crystal is integral in structure and well crystallized. The energy-dispersive spectrometry results indicate that the wafer of the CdGeAs2 crystal is closer to the stoichiometry. The IR transmittance of the wafer is ~48.6 % at 5.5 μm, and the maximum value is up to 51.6 % in the range of 2.3–18.0 μm. Etch pits of (001) face are observed and the density of the etch pits is evaluated to be 1 × 105 cm−2.

The ground state parameters of interest such as the lattice constants, band structure, bulk modulus and elastic constants are calculated for chalcopyrite CdSiP2 using density functional theory (DFT). Detailed comparisons are made with published experimental and theoretical data and show generally good agreement. Based on the results above, we also presented the thermodynamic properties of CdSiP2 using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. Finally, we have successfully obtained the variations of the relative volume V/V0, thermal expansion coefficient α, heat capacities C, Debye temperature Θ and Gruneisen parameter γ as a function of the pressure and temperature.

A CdSiP 2 single crystal measuring 15 mm in diameter and 35 mm in length was grown by the modified vertical Bridgman method adopting a specially designed double-walled quartz ampoule. The as-grown crystal was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), infrared (IR) and visible–near infrared (VIS–NIR) spectrophotometers and X-ray photoelectron spectroscopy (XPS). It is found that multiple diffraction peaks of a (101) cleavage face are evident and parallel growth steps on the face are observed. The XRF result indicates that the chemical composition of the as-grown crystal is close to the ideal stoichiometry. The IR transmittance of a sample with 2 mm thickness is about 48% in the range from 10,000 to 1500 cm −1 . The VIS–NIR spectrum shows that the short wave absorption edge is at about 576 nm and the calculated band gap is about 2.15 eV. The binding energies of the Cd 3d 3/2 , Cd 3d 5/2 , Si 3d and P 2p core levels are determined to be 411.8 eV, 405.1 eV, 101.1 eV and 129.5 eV, respectively. These results show that the quality of the as-grown crystal is good and the double-walled quartz ampoule technique is promising for the growth of high-quality CdSiP 2 single crystals.

A crack-free CdGeAs2 single crystal 15 mm in diameter and 50 mm in length was grown in a three-zone tubular furnace by the modified vertical Bridgman method. During the annealing processes, the effects of treatments with different atmosphere, different temperatures and time were investigated. The as-grown and annealed wafers were characterized using X-ray diffractometer (XRD), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and IR microscope. Conclusively, the results confirm annealing could improve the optical qualities of as-grown CdGeAs2 crystal. The best result was obtained under cover-up with CdGeAs2 polycrystalline powder at 450 °C for 150 h and the IR transmittance of the wafer measured by FTIR was up to 48.65% nearby 5.5 μm and exceeded 50% in the range of 8–12 μm. Additionally, the monolithic homogeneity of the crystal has also been greatly improved after annealing under cover-up with polycrystalline powder.

The causes of non-stoichiometry in both synthesis and growth process of ZnGeP 2 (ZGP) have been studied. The effects of mechanical oscillation (MO) and gradient cooling (GC) techniques employed in the synthesis of ZnGeP 2 polycrystals have been investigated. X-Ray Diffraction analysis (XRD) has identified that phosphorus was the main loss component. The growth of ZnGeP 2 crystal was carried out in a three-section vertical Bridgman (VB) furnace. A certain amount of phosphorus was added to ZnGeP 2 polycrystals before growth. The temperature gradients were controlled at 10–15 °C/cm within crystallization zone. A ZnGeP 2 crystal with the size of Φ 25 mm×55 mm was obtained. The proportions of P, Ge and Zn in the grown crystal were measured with Energy Dispersive Spectrometer (EDS). The results showed that the grown crystal has good stoichiometry and homogeneity. Infrared transmittance and absorption spectra show that the crystal has low absorption in 2.0–10.0 μm range. Absorption contour maps by automatic infrared microscope demonstrate that optical homogeneity of grown crystal is good.

A theoretical study of the structural, elastic and thermodynamic properties of the cubic zinc-blende (ZB) structure InN are presented in this paper by performing first principles calculations within local density approximation. The values of lattice constant, bulk modulus and its pressure derivatives and elastic constants are in excellent agreement with the available experimental data and other theoretical results. It is found that the ZB structure InN should be unstable above 20 GPa mechanically. The pressure and temperature dependencies of the bulk modulus, the heat capacity and the thermal expansion coefficient and the entropy S, as well as the Gruneisen parameter are obtained by the quasi-harmonic Debye model in the ranges of 0–1500 K and 0–25 GPa.

We present an ab initio theoretical study of the electronic, linear and nonlinear optical properties of CdGeAs{sub 2} using a pseudopotential plane-wave method. Specifically, we evaluate the band structure, density of states, charge density, the dielectric function {epsilon}({omega}) and the second harmonic generation response susceptibility {chi}{sub 312}{sup (2)}(-2{omega};{omega},{omega}) over a large frequency range. As LDA underestimates the band gap, we have applied the GW approximation method to calculate the quasiparticle band structure and obtain an energy band gap in agreement with experiment. In this case the opening of the gap due to the GW correction can be used as scissor shift to calculate the linear and nonlinear optical properties. The intra- and inter-band contributions to the imaginary part of {chi}{sub 312}{sup (2)}(-2{omega};{omega},{omega}) are presented over a broad energy range. It is found that the small energy gap semiconductor CdGeAs{sub 2} has larger values of {epsilon}{sub 1}(0) and {chi}{sub 312}{sup (2)}(0) than other chalcopyrite structures. - Graphical abstract: Calculated total imaginary part of {chi}{sub 312}{sup (2)}(-2{omega};{omega},{omega}) spectra along with the intra-(2{omega})/(1{omega}) and inter-(2{omega})/(1{omega}) band contributions. Highlights: Black-Right-Pointing-Pointer We find that the charge density around the cation Cd of CdGeAs{sub 2} is spherical. Black-Right-Pointing-Pointer We do not have to rely on experimentalmore » gap to determine the self-energy. Black-Right-Pointing-Pointer It is the first time we have calculated the SHG susceptibility using pseudopotential plane-wave. Black-Right-Pointing-Pointer The SHG susceptibility beyond zero frequency was calculated.« less

High-purity, single-phase CdSiP2 polycrystalline materials were synthesized directly from the constituent elements by a new method without graphite boat sealed in silica ampoule. The problem of explosions was solved by careful control of the heating and cooling cycle and adopting the two-zone rocking furnace with specially designed temperature profile. Mechanical and temperature oscillations as well as gradient cooling were introduced in the synthesis process. The mechanism and advantages of this new method are discussed. X-ray diffraction (XRD) analysis and Energy dispersive X-ray (EDX) microanalysis both indicated that the synthesized compound is high-quality CdSiP2 polycrystalline material.

A high quality ZnGeP 2 (ZGP) single crystal 22 mm in diameter and 70 mm in length was grown by a modified vertical Bridgman method. The as-grown and annealed crystals were characterized using XRD, IR spectrophotometers, positron annihilation lifetime (PAL), Hall Effect and resistivity measurements. It is found that there was a cleavage face {2 0 4} along the appearance face on the as-grown crystal. After annealing the crystal, the width of XRD rocking curve of the annealed crystal was decreased, the intensity was high and the symmetry was better than that of the as-grown crystal. The IR transmission spectrum indicated that annealing decreases significantly the optical absorption in the region of 1.3–2.6 μm and transmittance exceeds 57% in the range of 3–8 μm. PAL results showed that single zinc vacancies were unstable since they aggregated with each other after annealing under zinc vapor at 500 °C, and both the number of single zinc vacancy and the size of large vacancy decreased under cover-up with ZGP polycrystalline powder at 600 °C. The Hall effect and resistivity measurement results showed that the ZGP crystal has p-type conductivity; after annealing with ZGP polycrystalline powder the carrier concentration was decreased to 10 10 cm −3 and resistivity was increased to 10 8 Ω cm. The above mentioned results demonstrated that annealing treatment improved significantly the optical quality of as-grown ZGP crystal; the proposed annealing process is effective and a promising new method to decrease of the point defects in the ZGP crystal.

Large, integral AgGa 1− x In x Se 2 ( x =0.6, 0.8) single crystals were grown from a melt. The polycrystalline charges were successfully synthesized from high purity elemental starting materials by the vapor transport method with the melt and temperature oscillation. The crystallization processes were carried out in two-layer quartz ampoules with ampoule rotation and the real-time temperature compensation technique. The quality of the as-grown crystals was characterized using a microscope, XRD, IR and vis–NIR spectrophotometers, etc. Cleavage faces of (1 1 2) were found, and high transmittance of the crystals in the mid-near IR region was revealed. The absorption edges of the materials are near 905 and 958 nm, and the calculated band gaps are about 1.37 and 1.29 eV. All the measurements confirmed the good quality of the grown crystals.

A chemical etching orientation method is suggested for the ZnGeP 2 crystals. Several polished faces of ZnGeP 2 crystals were etched in a certain etching solution. Some regular etch pits appeared on all samples. The indices of side facets of the etch pits were measured by X-ray rocking method, which mainly belong to {2 0 4}, {1 1 2} and {1 1 0}. Then the three crystallographic axes of the crystals were determined according to the angle relationship. Finally, optical parametric oscillator (OPO) devices were cut at the direction of θ =0° and φ =53°.

We have performed a first-principles study of structural, vibrational and dielectric properties of CdGeAs2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Calculations of the zone-center optical-mode frequencies (including longitudinal-optical/transverse-optical splitting), Born effective charge tensors for each atom, and dielectric constants, using density functional perturbation theory, are reported. The fully relaxed structural parameters are found to be in good agreement with experimental and other calculation data. All optical modes are identified and agree with infra-red and Raman measurements.

The growth procedures for CdSe crystal have been optimized by thermal analysis techniques and a high-quality single crystal with large size has been grown. CdSe crystal was determined to exhibit smooth interface growth based on Jackson’s model; the growth rate equation in the vapor phase method was built and the thermodynamic parameters (activation energy and rate constant pre-factor) in the growth equation were obtained by thermogravimetic analysis of the sublimation process of the crystal. The growth rate distribution curves under various temperature differences between the source and growth region of growth ampoule were obtained, and then the growth procedures such as temperature difference, growth temperature and pulling rate were optimized. Using the optimizing vapor phase growth technique, a single crystal with 26 mm diameter and 45 mm length has been grown, and it was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive analyzer of X-ray and IR spectrophotometers. The results show that the as-grown CdSe ingot has prefect crystallinity, good homogeneity and high transmittance, which showed that the vapor phase growth technique optimized by thermal analysis was a promising growth method for high-quality CdSe single crystal.

A large, crack-free CdGeAs2 single crystal measuring 15 mm in diameter and 45 mm in length was grown in a vertical three-zone tubular furnace by a modified vertical Bridgman method, i.e. quasi-seed technique with small temperature gradient and descending quartz ampoule. High-purity, single phase CdGeAs2 polycrystallite for crystal growth was synthesized using a rocking furnace with temperature oscillation techniques. Various measuring means, including X-ray diffractometer(XRD), Fourier transform infrared spectroscopy(FTIR), and Field emission scanning electron microscope(FE-SEM) were adopted to characterize the as-grown crystal. It is found that the cleavage plane of the as-grown crystal is {1 0 1} face; the crystal is integrated in structure and crystallized well; etch pits in the shape of pentagon on (1 1 2) face have been observed for the first time using the new preferential etchant we prepared. All these results encouragingly indicate that the modified vertical Bridgman method is a convenient and effective way for high quality CdGeAs2 crystal growth.

High-pure, single-phase, free of voids and high mass density AgGaS 2 polycrystalline was synthesized by a new method, i.e. two-temperature zone vapor-transporting together with the mechanical and melt temperature oscillation method (TVMMTOM), directly from high-purity (6 N) elements silver, gallium and sulfur with excess sulfur. The mechanism and advantages of the new method for synthesizing high-quality AgGaS 2 were discussed. It is found that the polycrystalline material synthesized by the new method is superior to that synthesized by the conventional method, what is more the new method can avoid the explosion of the synthetic quartz ampoule. Adopting the modified Bridgman method an integral and crack-free AgGaS 2 single crystal with diameter of 14 mm and length of 63 mm has been obtained. It was found that there was a (1 0 1) cleavage face and the four order X-ray spectrum of the {1 0 1} faces was observed. By the method of DSC analysis the melting and freezing points of the AgGaS 2 single crystal were about 995 and 955 °C. The transmission spectra of the AgGaS 2 sample of 10 × 8 × 2 mm 3 were obtained by means of UV and IR spectrophotometer. The limiting wavelength was 470 nm and the band gap was 2.64 eV. It can be found in the infrared spectrum that the infrared transmission was above 55% from 4000 to 800 cm −1 , and the infrared transmittance of the crystal is up to 63% at 10.6 μm, which is higher than that of the crystal grown using polycrystalline materials synthesized by the conventional method. The value of α in 10.6 μm was 0.267 cm −1 . Above mentioned results showed that the crystal was of good quality and TVMMTOM is preferable for synthesizing high-quality AgGaS 2 polycrystalline materials.

Good quality AgGa1−xInxSe2 (x=0.1–0.3) single crystals with 20 mm diameter and 60 mm length have been grown by an improved Bridgman method, i.e. descending ampoule with rotation and the real-time temperature compensation technique. The melt temperature oscillation method (MTOM) was used to synthesize high-purity single-phase AgGa1−xInxSe2 polycrystal that is free of voids. The crystallization process was carried out in the two-layer quartz ampoule with a seed pocket. The temperature gradient at the growth interface in the furnace was normally 20 °C cm−1 in the open bore, while it was 15 °C cm−1 with the ampoule in the furnace. The quality of the as-grown crystal was characterized by using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), infrared (IR) spectrophotometer, etc. It was found that there is a {1 1 2} cleavage face in the as-grown crystal and the homogeneous growth steps on the {1 1 2} face were observed. The four-order diffraction peaks of the {1 0 1} faces were evident. The transmittance of the crystal sample of 2 mm thickness is up to 65% in the region of 700–6500 cm−1. The results demonstrated that the improved new growth method of AgGa1−xInxSe2 single crystals is promising and the quality of the grown crystals is good, and after annealing, the crystals can be used for IR nonlinear optical devices.

A good quality ZnGeP2 (ZGP) single crystal 15 mm in diameter and 40 mm in length was grown in a vertical three-zone tubular furnace by the modified Bridgman method, i.e. real-time temperature compensation technique (RTTCT) with descending ampoule. The starting material is high-pure and single-phase polycrystal of ZnGeP2 synthesized by the single-temperature zone and mechanical oscillation method (STZMOM). The as-grown single crystal was characterized by various methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analyzer of X-ray (EDAX), and IR and UV spectrophotometers. It is found that there is a cleavage face of (1 1 2) and second-order XRD peaks of the {1 1 2} faces are observed, the IR transmittance of a sample of 2 mm thickness is above 55% in the range from 6000 to 800 cm−1, the absorption edge is near 612.5 nm and the band gap is about 2.02 eV. The absorption coefficient (α) is within 0.015–0.022 cm−1 at the spectral region 2–8 μm. The crystal has a stoichiometry ratio Zn:Ge:P=1:1.12:1.91 which is close to the ideal stoichiometry ratio of 1:1:2. All results demonstrate that the modified growth method is a new and promising method for the ZGP single crystal and the quality of as-grown crystal is good.

Based on Zhao's semi-SCF d-orbit wave functions model of free Co2+ ions, the superposition crystal field model and Macfarlane's perturbation loop method, the distances of the Co–O band in a SrLaAlO4:Co2+ crystal were determined by calculating the experimental optical spectra and EPR parameter. The agreement between the calculated result and the experimental data showed quantitatively that Co–O distances perpendicular to and parallel with the C4 axis were 0.1892 and 0.2139 nm, respectively.

In order to prevent the vanadium crossover and preferential water transfer in all-vanadium redox flow battery (VRFB), three methods – electrolyte soaking, oxidation polymerisation and Electrodeposition, were used to modify Nafion 117 membranes using pyrrole. The surface of the modified membranes was uniform and even, and the membranes were characterised in terms of morphology, membrane area resistance, vanadium permeability and water transfer property. The properties of all the modified membranes were improved greatly. The membranes modified by Electrodeposition showed a best combination of the membrane resistance, vanadium permeability and water transfer property, the experimental results showed that the V(IV) ion permeability of polypyrrole modified Nafion membranes by Electrodeposition at the conditions of 0.025 mA cm−2 and 0 °C for 60 min reduced more than 5 times from 2.87 × 10−6 cm2 min−1 to 5.0 × 10−7cm2 min−1, and the water transfer property decreased more than 3 times from 0.72 ml/72 h cm2 to 0.22 ml/72 h cm2. All above properties made the modified Nafion membranes more applicative in the VRFB system. This paper also reported other methods for Nafion membrane modification and the influences of the deposition conditions on the properties of the membrane selectivity and water transfer. Keywords: Vanadium redox flow battery, Nafion membranes modified by polypyrrole (PPR), Electrodeposition, Ion permeability, Water transfer property