Optical inhomogeneities in Li2B4O7 single crystals

Lithium tetraborate, Li₂B₄O₇ (LTB) crystals were grown by Czochralski technique. It belongs to tetragonal system with lattice parameter a = b = 9.479 Å, c = 10.286 Å. Transmission range of this crystal is 170 nm – 3300 nm. This material has attracted much attention because of its application in higher harmonic generation of Nd:YAG laser and radiation dosimetry. The grown crystals were characterized for their optical inhomogeneity using etch pit study, hardness, conoscopy, interferometry, and UV‐VIS transmittance techniques. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of pure and Co2+‐doped Li2B4O7 single crystals

Pure and Co‐doped Li₂B₄O₇ (LBO) single crystals were grown by the Czochralski method. Starting concentrations of Co₂O₃ in the melt were: 0.5, 0.85 and 1 mol% relative to Li₂CO₃. Technological factors affecting the quality of both crystals were discussed. Optical absorption and EPR spectra were analyzed to define the oxidation states and lattice sites of cobalt ions. It was shown that Co²⁺ ions enter LBO crystal at octahedral Li⁺ site positions. Low‐temperature EPR measurements revealed that two types of Co²⁺ complexes can be distinguished in the Li₂B₄O₇:Co crystals. Additional absorption calculated for γ‐irradiated crystals showed V_k type defects suggesting the creation of cation vacancies during growth. The concentration of the defects decreases with an increase of intentional Co concentration. Introduction of cobalt ions to LBO crystal is limited probably by the formation of cobalt ion pairs or by the entrance of cobalt as Co⁺. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crack resistance and atomic structure of Li2B4O7 single crystals

The nature of destruction of single crystals of lithium tetraborate Li₂B₄O₇ under the action of a concentrated load is investigated. It is established that planes of easy crack propagation in Li₂B₄O₇ single crystals are the (100), (010), (001), and {111} planes. It is found that crack propagation occurs in each case along the atomic layers that are linked by bridge oxygen atoms between main structural units (B₄O₉) and, therefore, are most weakly bound.     

Growth and optical homogeneity investigations of Fe and Fe:Mn codoped LiNbO3 crystals

Lithium niobate (LiNbO₃) crystals doped with Fe and Fe:Mn were grown by Czochralski technique. The doping concentrations of Fe and Mn were optimized. Transmission studies reveal broad absorption band centered at 488 nm. The UV cutoff observed for Fe doped LiNbO₃ is 358 nm whereas for Fe:Mn codoped LiNbO₃ is 352 nm. This decrease in UV cutoff for Fe and Mn codoped LiNbO₃ compared to only Fe doped LiNbO₃ is due to the increase in Li/Nb ratio. Optical homogeneity was assessed using conoscopy and birefringence interferometry. Dark and photo conductivity measurements prove that LiNbO₃ is a negative photo conducting material. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal expansion,pyroelectricity and linear optical properties of Li2SeO4·H2O and Li2SO4·H2O

Large single crystals of polar Li₂SeO₄·H₂O were grown at 343 K from aqueous solution. Temperature dependent thermal expansion coefficients of Li₂SeO₄·H₂O and Li₂SO₄·H₂O were determined within the temperature range 133 K–313 K and coefficients of the pyroelectric effect within the temperature range 183–343 K. Refractive indices between 365 nm and 1530 nm as well as unpolarized absorption spectra of Li₂SeO₄·H₂O and Li₂SO₄·H₂O were measured and phase‐matching curves for second harmonic generation were calculated. Both compounds allow type I and type II phase‐matching at wavelengths from about 650 nm to the near infrared region. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature Dependence of Static Electrical Conductivity of Li2B4O7 Crystals

Crystallography Reports - The static dc electrical conductivity of one-dimensional ion conductor Li2B4O7 (sp. gr. I41cd) has been investigated in the temperature range of 293–820 K using...     

Charge transport in Li2B4O7 in single crystal and glassy states

The electrophysical properties of Li₂B₄O₇ single crystals and glasses are studied in the temperature range 290–1100 K and the frequency range 1–1000 kHz. The strong frequency dispersion of ionic conductivity at temperatures close to room temperature is explained by the low-frequency hoppings of lithium ions from the basic to the interstitial positions. The dielectric relaxation accompanying the transport of lithium ions is analyzed within the framework of the Debye-Skanavi model. The minimum hopping length of Li⁺ ions and the height of the potential barrier between their closest positions are determined. The parameters obtained are compared with the known structural data.     

Li2B4O7晶体在SAW技术中的应用研究

采用CZ法生长了30×30mm3的Li2B4O7单晶体.对晶体的压电性能进行了研究,弹性系数的交叉分量少,数值相对较小;在(001)面内有较高的声波传播速度,其变化范围为6500～7080m/s,在[001]方向有较低的声波传播速度,大约为5160m/s;而压电性能表明在不同方向的机电耦合系数均比石英晶体相应参数大得多.对晶体谐振器和压控震荡器的性能进行了研究,发现其机电耦合系数近似石英的十倍,很适合用来制作宽频器件.晶体谐振器的频率温度特性为抛物线型,其转变温度在室温,在-10℃～55℃温度范围内频率变化为3×10-4,具有良好的频谱响应,其寄生频率高出主振180kHz,衰减大于30dB,完全能满足器件使用要求.晶体滤波器3dB带宽的相对宽为1;,而石英仅为0.4;.     

Structural,dielectric and optical properties of transparent glasses and glass-ceramics of SrBi2B2O7

Optically clear glasses of SrBi₂B₂O₇ (SBBO) were fabricated via the conventional melt-quenching technique. The amorphous nature of the as-quenched samples of this compound was confirmed by X-ray powder diffraction (XRD) studies. Its glassy nature was established by differential scanning calorimetry (DSC). However, the optical microscopy revealed the presence of isolated hexagonal shaped crystallites especially at the edges of the as-quenched glasses. The glass plates that were heat-treated around the onset of the glass transition temperature (670 K) for 12 h yielded transparent (～60% transmission) glass-ceramics of SrBi₂B₂O₇ (SBBO) with well defined microstructure. These were found to be textured associated with an orientation factor of about 0.77 (77%). The optical transmission studies carried out in the 100–1200 nm wavelength range confirmed both the as-quenched and heat-treated samples to be transparent from 400 to 1200 nm. The dielectric properties of the as-quenched as well as the heat-treated (670 K/12 h) samples were studied as a function of frequency (100 Hz–10 MHz) at various temperatures (303–873 K). The dielectric dispersion at higher temperatures in the as-quenched glass was rationalized using Jonscher’s dielectric dispersion relations. The prefactor A(T) and the exponent n(T) in the Jonscher’s expression were found to be maximum and minimum respectively around the crystallization temperature (T_cr) of the as-quenched SBBO glasses.     

Behavior of LiOH·H2O crystals obtained by evaporation and by drowning out

In the present work, the behavior of crystals derived from two different crystallization methods applied in a concentrated aqueous lithium salt solution was studied. The LiOH·H₂O crystals obtained by a simple evaporation (Crystal I) differed in terms of morphology and solubility from those precipitated from lithium hydroxide solutions by addition of ethanol as a co‐solvent (Crystal II). Solubility of Crystal II at different temperatures (15 to 35°C) and mass ratios of ethanol to water (0 to 0.1) was determined. Polymorphic like behavior of these crystals was evidenced from X‐ray diffraction patterns. Measurement of density, refractive index, absolute viscosity and electrical conductivity of saturated solutions are reported. A thermodynamic analysis in terms of the Chen model for the calculation of activity coefficients, indicate that the polymorphic system in water and in water + ethanol (ethanol/water ratio 0.1) is enantiotropic. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

EPR and optical studies of Mn2+ ions in Li2O–Na2O–B2O3 glasses – An evidence of mixed alkali effect

EPR and optical absorption spectra of 0.5 mol% MnO₂ doped xLi₂O–(30 − x)Na₂O–69.5B₂O₃ (5 ⩽ x ⩽ 25) glasses have been studied. The EPR spectra exhibit resonance signals characteristic of Mn²⁺ ions. The resonance signal at g ≅ 2.0 is due to Mn²⁺ ions in an environment close to octahedral symmetry, whereas the resonances at g ≅ 4.3 and g ≅ 3.3 are attributed to the rhombic surroundings of the Mn²⁺ ions. The ionic character (A), the number of spins participating in resonance (N), optical band gap energies (E_opt) and Urbach energies (ΔE) show the mixed alkali effect (MAE) with composition. The present study gives an indication that the size of alkalis we choose, is also an important contributing factor in showing the MAE. The variation of N with temperature obeys the Boltzmann law. The optical absorption spectra show a single broad band at ∼21 000 cm⁻¹ corresponding to the transition ⁶A_1g(S) → ⁴T_1g(G) which exhibits a blue shift with x. The theoretical values of optical basicity (Λ_th) have also been evaluated.     

Crystal growth of zirconium‐doped KTiOPO4 crystals in the K2O‐P2O5‐TiO2‐ZrF4 system

Zirconium‐doped KTiOPO₄ (KTP) crystals were grown using a high temperature flux method in the K₂O‐P₂O₅‐TiO₂‐ZrF₄ system. The dopant content in the single crystals with general composition KTi_1‐xZr_xOPO₄ (where x = 0 – 0.026) strongly depends on zirconium concentration in the homogeneous melts. AES‐ICP method and X‐ray fluorescence analysis were used to determine the composition of the obtained crystals. Phase analyses of the products were performed using the powder XRD. The structures of KTiOPO₄ containing different quantities of Zr were refined on the basis of single crystal XRD data. Applying ZrF₄ precursor for zirconium injection into the flux allowed growing the zirconium‐doped KTP crystals at 930–750°C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and optical properties of Co doped TlGaS2 crystals

In this study, Co doped TlGaS₂ single crystals which belongs to the class of A^IIIB^IIIX₂^VI have been investigated by means of XRD, temperature dependent dark and illuminated conductivity, Space Charge Limited Currents and absorption measurements. The room temperature conductivity and trap concentration values were about 10^‐8 (Ω‐cm)^‐1 and 7.5 × 10¹³ cm^‐3, respectively. From the temperature dependent conductivity measurements, two activation energies namely 271 and 12 meV have been determined in the high and low temperature regions, respectively. The trap level at 271 meV that was determined by the dark temperature dependent conductivity measurement has also been verified by Space Charge Limited Currents analysis. The absorption measurements have showed that the layered compound had indirect and direct band gaps and the values were determined to be 2.49 and 2.56 eV, respectively. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure and optical fixing holographic storage of Mg:Mn:Fe:LiNbO3 crystals

Mg:Mn:Fe:LiNbO₃ crystals were grown by the Czochralski method. The defect structure was analyzed by UV‐vis spectra and IR spectra. The holographic storage of Mg:Mn:Fe:LiNbO₃ crystals was measured by the two color fixed method. The results show that with the increase of MgO doping concentration, the writing time becomes shorter, the dynamic range decreases, photorefractive sensitivity increases and fixing diffraction efficiency decreases. When the MgO doping concentration exceeds 4.5 mol%, the fixing diffraction efficiency approaches zero. The effect of doping Mg ions on the holographic storage properties of Mn:Fe:LiNbO₃ crystals is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrooptical coefficients and temperature and pressure derivatives of the elastic constants of tetragonal Li2B4O7

New values for the following properties of tetragonal Li₂B₄O₇ are reported: dielectric, electrostrictive, electrooptic, elastic, thermoelastic and piezoelastic constants, coefficients of thermal expansion and indices of refraction. These values are considered to be of superior precision compared to earlier published data. Most elastic constants possess positive temperature derivatives. This anomalous behaviour is not reflected in the pressure derivatives. The electrooptic effects are not large enough to compete with other materials used for technical applications.     

Evolution of nanocrystalline BaBi2Nb2O9 in Li2B4O7–BaO–Bi2O3–Nb2O5 glass system

Transparent glasses and glass nano crystal composites (GNCs) of various compositions in the system (100 − x)Li₂B₄O₇–x(BaO–Bi₂O₃–Nb₂O₅) (where x = 10, 20, and 30 in molar ratio) were fabricated via splat-quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction and transmission electron microscopic (TEM) studies confirmed the formation of layered perovskite BBN via a fluorite like phase. TEM studies revealed the presence of 10 nm sized spherical crystallites of fluorite like BaBi₂Nb₂O₉ phase in the glassy matrix of Li₂B₄O₇ (LBO). The influence of composition on the dielectric and the optical properties (transmission, optical band gap) of these samples has been investigated.     

Al2O3衬底上生长ZnO薄膜的结构和光学特性

用脉冲激光沉积法在Al2O3(0001)衬底上沉积了ZnO薄膜.衬底温度分别为300℃、400℃、500℃、600℃和700℃.利用X射线衍射(XRD)和光致发光谱(PL)对薄膜的结构和光学性能进行研究.X射线衍射的结果表明在不同温度下生长的ZnO薄膜均具有高度c轴择优取向,衬底温度400℃时,膜的应力较小质量较高.ZnO薄膜有很强的紫外发光峰,紫外发光峰的强度与衬底温度密切相关,并发现当衬底温度从300℃增到400℃时,紫外发射峰出现6nm的蓝移.     

Polymorphism of Li4P2O7: New Modification and Identification of Structural Subfamilies by Topology and Symmetry Analysis

Crystallography Reports - Crystals of a new polymorph of pyrophosphate Li4P2O7 were prepared by the hydrothermal synthesis route due to the effect of mineralizing agents. The investigation of the...     

Acoustic damping in Li2O–2B2O3 glass observed by inelastic X-ray and optical Brillouin scattering

The dynamic structure factor of lithium-diborate glass has been measured at several values of the momentum transfer Q using high resolution inelastic X-ray scattering. Much attention has been devoted to the low-Q-range, below the observed Ioffe–Regel crossover q_IR ≃ 2.1 nm⁻¹. We find that below q_IR, the linewidth of longitudinal acoustic waves increases with a high power of either Q, or of the frequency Ω, up to the crossover frequency Ω_IR ≃ 9 meV that nearly coincides with the center of the boson peak. This new finding strongly supports the view that resonance and hybridization of acoustic waves with a distribution of rather local low frequency modes forming the boson peak is responsible for the end of acoustic branches in strong covalent glasses. Further, we present high resolution Brillouin light-scattering data obtained at much lower frequencies on the same sample. These clearly rule out a simple Ω²-dependence of the acoustic damping over the entire frequency range.     

Growth and characterization of Mn2+ doped calcium l‐tartrate crystals

Single crystals of Mn²⁺ doped calcium levo‐ tartrate tetrahydrate (CLTT) were grown by single diffusion gel growth technique in silica hydro‐gel media. The doping of Mn²⁺ was varied by mixing 0.001M, 0.005M, 0.01M, 0.05M, and 0.1M solutions of MnCl₂ with 1M CaCl₂ solution in equal volumes in the supernatant solutions. The actual amount of Mn²⁺ doping in CLTT crystals was estimated by ICP (Inductively Coupled Plasma) technique. The powder XRD of the samples suggested no significant change in the unit cell dimensions and the presence of any extra phase. The FT‐IR spectra indicated the presence of water molecule, O‐H bond, C‐O bond and carbonyl C=O bond. The EPR spectra confirmed the presence of Mn²⁺ ions in the crystals. The variation of the dielectric constant with temperature confirmed the earlier results of pure calcium tartrate crystals and indicated the ferroelectric nature of the doped crystals. As the amount of doping of Mn²⁺ increased the value of dielectric constant increased. The results are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)