首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献,搜索用时 203 毫秒
1.
唐玲云  刘景  肖万生 《中国物理 C》2005,29(Z1):109-111
利用同步辐射能量色散X射线衍射技术对SrF2进行了高压相变实验研究. 实验以Ar作为传压介质, 以获得准静水压条件. 实验用红宝石荧光法标定样品压力, 得到的最高压力为44.2GPa. 在实验压力范围内, SrF2在11.2GPa时发生了从立方晶系到正交晶系的相变, 通过拟合相变前后的P-V状态 方程, 得到立方SrF2的体弹模量为70.0(5.0)GPa, 正交SrF2的体弹模量为198.3(15.2)GPa. 卸压到零压时, SrF2回到立方相结构.  相似文献   

2.
通过温度梯度法制备了Bi2O3:BaF2以及BiF3:BaF2晶体.在Bi2O3:BaF2晶体中观察到了发光峰位于961 nm,半高宽202 nm的超宽带红外发光.在BiF3:BaF2晶体中检测到Bi2+和Bi3+可见区的发光,但是没有观察到红外发光.通过γ射线辐照实现了BiF3:BaF2晶体的近红外发光, 发光峰位于1135 nm,半高宽192 nm.讨论了Bi2O3和BiF3掺杂BaF2晶体的红外发光的机理.  相似文献   

3.
吴叶青  苏良碧  徐军  陈红兵  李红军  郑丽和  王庆国 《物理学报》2012,61(17):177801-177801
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   

4.
在BaF2中掺入1% mol的BaF3结晶出BaF2(La)晶体,经测试,此晶体闪烁发光快成份的强度比纯BaF2晶体不减弱,而发光慢成份被抑制约4倍,耐辐照能力可以达到106rad,表明新晶体有希望满足未来高能物理实验的要求.  相似文献   

5.
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   

6.
兰宇丹  何立明  丁伟  王峰 《中国物理 B》2010,19(4):2617-2621
本文对不同初始温度下,H2/O2混合物等离子体中主要粒子随时间发展的演化规律进行了数值模拟,得到了放电后等离子体中主要带电粒子和中性粒子密度随时间的变化规律.计算结果表明,H2/O2混合物等离子体中主要活性粒子密度随时间的增加减小,化学反应达到平衡所需的时间随初始温度升高逐渐减少.  相似文献   

7.
王晓坡  宋渤  吴江涛  刘志刚 《物理学报》2010,59(10):7158-7163
采用反转法计算得到了O2-CO2混合气体新的势能参数.在此基础上,根据分子动力学理论,计算了混合气体在零密度下的输运性质,包括黏度系数、热扩散系数和热扩散因子,计算的温度范围为273.15—3273.15 K.与实验值比较表明,计算结果可以满足实际工程应用.  相似文献   

8.
将BaF2晶体与半导体探测器组成的望远镜用于12C(46.7MeV/u)入射核反应中前方向产物的测量,用ΔE-E方法和快慢成分关联方法进行了粒子鉴别.同时还研究了BaF2晶体对多种离子的响应.  相似文献   

9.
对Mg2(BH4)2(NH2)2的脱氢机理展开系统的理论研究发现相对于分子内的脱氢过程,分子间的脱氢过程在热力学和动力学方面都是比较有利的. Mg2(BH4)2(NH2)2脱氢过程的第一步是BH4-中的B-Hδ-和NH2-中  相似文献   

10.
对UO2在300~3000 K的分子动力学模拟结果的讨论,计算得到了体系的晶格参数均方位移和UO2中铀和氧的速度自相关函数得到的声子密度.在模拟计算中,采用了两种原子相互作用势,其中由Basak势计算优化的晶格参数与报道的实验数据符合的非常好;两种势函数得到的均方位移和Bredig态都比较好.最后,讨论了UO2的声子密度,随着温度的逐渐升高,声子密度的强度是逐渐增大的,并且,振动曲线是随着温度的增加逐渐向低频部分平移并变得逐渐平稳;氧原子的  相似文献   

11.
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   

12.
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   

13.
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   

14.
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   

15.
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   

16.
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   

17.
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   

18.
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   

19.
刘春梅  葛妮娜  付志坚  程艳  朱俊 《中国物理 B》2011,20(4):45101-045101
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   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号