共查询到19条相似文献,搜索用时 203 毫秒
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采用坩埚下降法生长了Yb: CaF2-SrF2晶体,测试了该晶体的吸收和荧光光谱 以及在不同温度下晶体的热扩散系数和热膨胀系数,并且计算了晶体的热膨胀系数以及在常温下的热导率. 采用对比的方法,对晶体的吸收光谱,荧光光谱,热学性能进行了分析.从吸收和荧光光谱结果表明: 在掺杂相对较高浓度的SrF2的混晶中, Yb3+吸收截面和发射截面比较大. Yb: CaF2-SrF2 (19%)晶体在1040 nm附近的发射截面比较大,光谱也比较宽. 这说明在掺杂相同浓度Yb时,混晶中CaF2, SrF2的比例不同,晶体的光谱性质不同, 主要原因是在混晶中晶体的无序度不同,晶体对称性降低,形成低对称光学中心. 从热扩散系数计算的热导率结果看出晶体具有比较好的热导率. 相似文献
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利用金刚石对顶砧高压装置和激光双面加热技术, 以经700°C热处理后的吉林长白山硅藻土作为非晶态SiO2样品,在0—4GPa, 1000—1300K温压条件下开展同步辐射X射线衍射原位测试(EDXD方法), 研究非晶态SiO2在高温高压条件下的结晶转变方式. 测试结果表明, 在0.8—2.4GPa, 1000—1300K温压条件下, 非晶态SiO2转变成α-石英而非β-石英或方石英, 其结晶温度较常压下非晶态SiO2晶化所需温度明显较低, 表明压力有利于降低非晶态SiO2转变的活化能, 并与常压下的结晶产物不同. 在3—4GPa, 1300K温压条件下, 非晶态SiO2和石英均转变成了柯石英. 相似文献
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Peter W. Mirwald George C. Kennedy 《Journal of Physics and Chemistry of Solids》1980,41(10):1157-1160
The phase diagram of SrF2 to 50 Kbars and 1900°C, obtained primarily by differential thermal analysis (d.t.a.), is presented. In analogy to the isostructural compound CaF2, three solid phases, α, β, γ-SrF2, as well as the liquid field, have been located. Thermochemical data (dT/dP, ΔV, ΔS) of the α-β and α-γ boundaries, and the melting curve are given. A tentative phase diagram for the isostructural compound BaF2 is proposed. In addition, the first compression data for SrF2 to 40 Kbars are reported. The bulk modulus, its pressure derivative, and the Grüneisen constant of SrF2, CaF2 and BaF2 are compared. 相似文献
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The present paper reports a comprehensive and complementary study on structural, electronic and phonon properties of face centered cubic fluorites, namely CaF2, BaF2 and SrF2, using first principles density functional calculations within the generalized gradient approximation. The calculated lattice constants and bulk modulus are in good agreement with available experimental data. The analysis of band structure and density of states confirms the ionic character for all the three fluorides. The phonon dispersion curves and corresponding phonon density of states obtained in the present work are consistent with the available experimental and other theoretical data. The LO-TO splitting is maximum for CaF2, which confirms that the ionicity is maximum in the case of CaF2. The phonon properties for SrF2 have been calculated for the first time. 相似文献
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The results of electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) studies of a self-trapped hole (VK center) in SrF2 are reported. The g-factor and hyperfine interaction constants were determined for the flourine nuclei forming the center and for those in the nearest three different sites. The values of hyperfine interaction constants are intermediate to the known values for CaF2 and BaF2. 相似文献
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We have studied polycrystalline brookite TiO2 using energy-dispersive X-ray diffraction at pressures up to 27.8 GPa and derived an ambient-pressure bulk modulus of 255 GPa using Birch-Murnaghan's equations of state with a fixed value of 4 as its first derivative. The transition from brookite-type to baddeleyite-type was observed to start at 15.8 GPa and finished at 22.8 GPa. Upon decompression, the α-PbO2 structure appeared at 3.5 GPa and the baddeleyite-type structure remained down to 1.6 GPa, the lowest pressure in the present work. 相似文献
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We report the results of electrical resistance measurements at high pressures on Cs2MoS4 and KTbP2Se6. The results of high pressure X-ray diffraction study of Cs2MoS4 are also presented. Interestingly, in the case of Cs2MoS4 the resistance vs. pressure follows the behavior of the absorption edge vs. pressure obtained from our optical measurements lending further support to a direct-indirect band crossing. In the case of KTbP2Se6,the phase transition at about 9.2 GPa is reflected in a sharp drop of the resistance. In addition we report the pressure dependence of the lattice constants as well as the equation of state of Cs2MoS4. 相似文献
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R.A. Secco H. LiuN. Imanaka G. AdachiM.D. Rutter 《Journal of Physics and Chemistry of Solids》2002,63(3):425-431
Impedance spectroscopy measurements and synchrotron X-ray diffraction studies of Sc2(WO4)3 at 400°C have been carried out as a function of pressure up to 4.4 GPa. Ionic conductivity shows normal decrease with increase in pressure up to 2.9 GPa, but then increases at higher pressures. The XRD results show that Sc2(WO4)3 undergoes pressure-induced amorphization at pressures coincident with the reversal in conductivity behavior. The loss of crystal structure at high pressure is consistent with growing evidence of pressure-induced amorphization in negative thermal expansion materials, such as Sc2(WO4)3. The increase in conductivity in the amorphized state is interpreted as the result of an increase in structural entropy and a concomitant reduction of energy barriers for ionic transport. 相似文献
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E.J. Bijvank A.G. Zandbergen-Beishuizen H.W. den Hartog 《Solid State Communications》1979,32(3):239-244
In this paper we report new results of EPR experiments on orthorhombic Gd3+-M+ complexes (M = Na, K, Rb and Ag) in SrF2. Special attention is payed to the second degree crystal field parameters B02 and B22 and a comparison with earlier results on corresponding complexes in CaF2 and BaF2 is made. We conclude that the main contributions to these crystal field parameters are of electrostatic nature. 相似文献
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K. Kinoshita 《Solid State Communications》2007,141(2):69-72
Up to now a Ni2In structure is a final step in the structural sequence of ionic AX2 compounds under high pressure. Powder X-ray diffraction experiments on BaH2 were performed at room temperature and high pressures up to 69 GPa. Successive phase transformations were observed to occur in two stages. The first was from the cotunnite to the Ni2In structure at 2.5 GPa. The second transition commenced at pressures around 50 GPa and was completed at 65 GPa. At the transition the arrangement of a cation sublattice changes from an hcp to a simple hexagonal lattice. This is the first observation of the post Ni2In phase. 相似文献
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We investigate the structural and thermodynamic properties of OsN2 by a plane-wave pseudopotential density functional theory method. The obtained lattice constant,bulk modulus and cell volume per unit formula are consistent with the available theoretical data. Moreover,the pressure-induced phase transition of OsN2 from pyrite structure to fluorite structure has been obtained. It is found that the transition pressure of OsN2 at zero temperature is 67.2 GPa. The bulk modulus B as well as other thermodynamic quantities of fluorite OsN2 (including the Gru¨neisen constant γ and thermal expansion α) on temperatures and pressures have also been obtained. 相似文献