共查询到20条相似文献,搜索用时 250 毫秒
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本文首次报道在3.15 GPa、1 200 ℃高温高压条件下合成出了SrSiO3:Eu3+Bi3+发光材料,并与常压合成产物相比较,研究了高温高压合成产物的结构以及合成压力、温度对发光特性的影响。结果表明,高压合成产物SrSiO3:Eu3+Bi3+的结构为膺正交(单斜)结构,而常压合成的为六角结构,高压使发光强度下降,量子发光效率下降了88%,谱线红移达756 cm-1,半值宽度也显著增加,发光性能的改变是由于压致结构的变化引起的。 相似文献
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介绍了VO2薄膜的相变原理,用磁控离子溅射法制备了VO2薄膜,并进行了X射线衍射和不同温度下的光谱透过率测量。在1.319 μm 连续波激光辐照下,实时测量了VO2薄膜的温度变化,以及由于温度变化引起相变后对激光透过率的变化。结果表明,入射到薄膜表面的平均功率为8.9 W、光斑直径2 mm时,激光出光480 ms后,VO2的温度从室温上升到约100 ℃,薄膜发生了相变,其对1.319 μm激光的透过率从相变前的48%降为相变后的28%。 相似文献
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研究了用HZ-B串列加速器的18MeV质子辐照对TiNi形状记忆合金R相变的影响,辐照在奥氏体母相状态下进行。示差扫描量热法(DSC)表明,辐照后R相变开始温度TsR和逆马氏体相变结束温度TfA随辐照注量的增加而降低。当注量为1.53×1014/cm2时,TsR和TfA分别下降6K和13K,辐照未引起R相变结束温度TsR和逆马氏体相变开始温度TfA的变化。表明辐照后母相(奥氏体相)稳定。透射电镜(TEM)分析表明辐照后没有引起合金可观察的微观组织变化。辐照对R相变开始温度TsR和逆马氏体相变结束温度Af的影响可能是由于质子辐照后产生了孤立的缺陷团,形成了局部应力场,引起晶格有序度的下降所造成的。 相似文献
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利用二级轻气炮加载下的冲击Hugoniot线(冲击波速度D-粒子速度u关系)和粒子速度剖面测量,结合基于密度泛函理论的平面波赝势计算研究了z切LiTaO3单晶的高压相变.实验发现,D-u关系在u=0.95km/s附近出现明显拐折;实测波剖面中25.9 GPa和32.6 GPa时观测到弹-塑性双波结构,而终态压力为42.7 GPa和53.0 GPa时则为三波结构.上述结果都清楚地表明z切LiTaO3单晶冲击相变的发生,相变起始压力约为37.9 GPa.同时,理论计算的菱形相(R3c对称群)压缩线与低压实验数据符合较好,而正交相(Pbnm对称群)压缩线则与扣除热压贡献的高压实验数据相符,由此推断z-切LiTaO3的高压相为正交结构.从实验和理论上澄清了z切LiTaO3的相变起始压力和高压相晶体结构的认识,研究工作亦对类似单晶材料的冲击相变研究有参考价值. 相似文献
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本文用差热分析、恒温热处理、X射线衍射等方法,对LiIO3在常压的相变过程做了进一步的研究。对于LiIO3的常压相变机制有了较为详尽的了解。并发现LiIO3在高温可相对稳定存在三个相:β,η和δ,它们可分别自行熔化,其熔点相应为:432℃,421℃和416℃,从它们的热经历和存在的温度范围,表明其稳定性顺序为β>η>δ。在室温干燥空气中,与α相和β相共存的还有ζ相,ζ相升温放热转变为β相。在α相存在的温区里,ζ相经过长时间热处理并不转变为α相,同时,ζ相转变为β相的温度比α相高。与α→β的情况相同,β对ζ→β也有诱导作用。而且的ζ存在对α→β也有促进作用。θ相(θ1与θ2)与γ相一样,是相变过程的中间过渡相。
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S. G. Jabarov D. P. Kozlenko S. E. Kichanov A. V. Belushkin A. I. Mammadov B. N. Savenko R. Z. Mekhtieva C. Lathe 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(3):546-551
The crystal structure of sodium niobate (NaNbO3) has been investigated by energy-dispersive X-ray diffraction at high pressures (up to 4.3 GPa) in the temperature range 300–1050 K. At normal conditions, NaNbO3 has an orthorhombic structure with Pbcm symmetry (antiferroelectric P phase). Upon heating, sodium niobate undergoes a series of consecutive transitions between structural modulated phases P-R-S-T(1)-T(2)-U; these transitions manifest themselves as anomalies in the temperature dependences of the positions and widths of diffraction peaks. Application of high pressure leads to a decrease in the temperatures of the structural transitions to the R, S, T(1), T(2), and U phases with different baric coefficients. A phase diagram for sodium niobate has been build in the pressure range 0–4.3 GPa and the temperature range 300–1050 K. The dependences of the unit-cell parameters and volume on pressure and temperature have been obtained. The bulk modulus and the volume coefficients of thermal expansion have been calculated for different structural modulated phases of sodium niobate. A phase transition (presumably, from the antiferroelectric orthorhombic P phase to the ferroelectric rhombohedral N phase) has been observed at high pressure (P = 1.6 GPa) and room temperature. 相似文献
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Takeshi Ohzeki Shinya Hasegawa Misa Shimizu Takuya Hashimoto 《Solid State Ionics》2009,180(17-19):1034-1039
Structural phase transitions in BaCeO3 have been investigated with combination of differential scanning calorimetry (DSC), dilatometry and high temperature X-ray diffraction with high sensitivity and resolution. In DSC curve at heating procedures, baseline shift, endothermic peak and another baseline shift were observed at 260 °C, 385 °C and 895 °C, respectively. From DSC curve at cooling procedure, it was revealed that all the baseline shifts and peak were reversible. No hysteresis was observed in the both baseline shifts indicating second order phase transition at 260 °C and 895 °C with variation of specific heat capacity, ΔCp, of 10 J/mol K and 7 J/mol K, respectively; whereas the order of the phase transition at 385 °C was revealed to be the first since hysteresis was detected around 370–385 °C. Variation of enthalpy, ΔH, at the phase transition was 45 J/mol. High temperature X-ray diffraction measurements have revealed that the crystal structure of BaCeO3 changes from primitive orthorhombic perovskite through body-centered one, rhombohedral distorted one to cubic one around 280 °C, 400 °C and 900 °C, showing correspondence with DSC curves. Dependence of molar volume on temperature estimated from high temperature X-ray diffraction showed agreement with thermal expansion behavior observed with dilatometry. 相似文献
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We studied the temperature dependence of the Raman spectrum of LiIO3, from room temperature up to t ~ 350°C. Two discontinuous changes in the spectrum are observed as temperature increases. The first one is reversible and occurs in a temperature range between 215°C and 260°C, depending upon sample origin (single crystal or powder) and thermal history. The second occurs at t ? 290°C and becomes irreversible once the samples are heated above 340°C. Each phase has a characteristic spectrum, distinct from that of the other two. Although the occurence of these phase changes are in complete agreement with studies made with X-ray diffraction and differential thermal analysis (DTA), it is at variance with previous Raman and infrared work which report no qualitative change in spectrum at the α ? γ phase transition. We believe this disagreement comes about because our measurements are the first ones so far to have actually passed through the transition. 相似文献
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G. Parthasarathy A.K. Bandyopadhyay S. Asokan E.S.R. Gopal 《Solid State Communications》1984,51(4):195-197
An irreversible pressure induced semiconductor-to-metal transition in bulk Ge20Te80 glass is observed at about 5 GPa pressure. The high pressure phase has a face centered cubic structure with a lattice constant 6.42 A° as deduced by X-ray diffraction studies on the pressure quenched samples. The temperature and pressure dependence of the electrical resistivity confirms the observed transition to be a semiconductor-to-metal transition. The temperature dependence of thermo electric power is also reported. 相似文献
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We investigated the high pressure phases of CdF2 by a joint theoretical and experimental study. The structural and electronic properties of CdF2 were extensively explored to high pressure by ab initio calculations based on the density functional theory. A structural phase transition from the fluorite-type (Fm-3m, Z=4) structure to the cotunnite-type (Pnma, Z=4) structure was estimated below 8 GPa, and this phase transition was examined by the high pressure experiments up to 35 GPa at room temperature. Both high pressure angle dispersive X-ray diffraction and Raman spectroscopy experiments provided convincing evidence to verify the phase transition. Our work makes clear pressure-induced phase transitions and structural information of CdF2 under high pressure. 相似文献
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Abstract X-ray diffraction studies on the kinetics and hysteresis of the structural phase transitions in lanthanides under pressures up to 58 GPa and temperatures between 200 and 520 K are presented. Estimates of the 0 K equilibrium transition pressures are derived from the pressure and temperature dependence of the activation free energies ΔaG. A comparison of critical radius ratios, Rws/R5p, for all the regular lanthanides at the various phase transitions shows simple systematics in the high pressure behaviour of the lanthanides. The “volume collapse” transitions in lanthanides are compared with the behaviour of the actinides and discussed with respect to f-electron delocalization. 相似文献
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Kaixue Wang Zili Kou Huan Ma Yanfei Wang Shanmin Wang Chao Xu Junwei Guan Duanwei He 《Solid State Communications》2012,152(6):540-544
This work presents a comprehensive study on phase transition in NaGaO2 under high pressure and temperature (P–T) conditions. X-ray diffraction (XRD) was used to identify the phase composition of the recovered samples. Our results revealed that NaGaO2 could undergo a structural phase transition from orthorhombic - NaGaO2 to hexagonal - NaGaO2 under high pressure and temperature. The pressure–temperature phase boundaries of NaGaO2 were determined up to 5 GPa and 2073 K. The hexagonal - NaGaO2 sample recovered from higher pressure and temperature exhibited a highly (003) preferred orientation. Besides, a reversible transition from - to - NaGaO2 was observed above 473 K under normal-pressure condition. The high-pressure melting curve of NaGaO2, for the first time, was measured by using in-situ thermal measurement. 相似文献
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Raman and optical absorption studies under pressure have been conducted on KTb(MoO4)2 up to 35.5 GPa. A phase transformation occurs at 2.7 GPa when the crystal is pressurized at ambient temperature in a hydrostatic
pressure medium. The sample changes to a deep yellow color at the transition and visibly contracts in theα-axis direction. The color shifts to red on further pressure increase. The Raman spectral features and the X-ray powder pattern
change abruptly at the transition indicating a structural change. The pressure-induced transition appears to be a property
of the layer-type alkali rare earth dimolybdates. However, the color change at the transition in KTb(MoO4)2 is rather unusual and is attributed to a valence change in Tb initiated by the structural transition and consequent intervalence
charge transfer between Tb and Mo.In situ high pressure X-ray diffraction data suggest that phase II could be orthorhombic with a unit cell having 3 to 4% smaller
volume than that of phase I. 相似文献