共查询到20条相似文献,搜索用时 171 毫秒
1.
2.
3.
4.
5.
6.
7.
8.
在10—800K的温度范围内用X射线衍射方法测量了DyMn2Ge2化合物的晶格常数与温度的变化关系,观察到高温时DyMn2Ge2由顺磁状态到反铁磁状态的自发磁相变伴随着晶格常数a的负的磁弹性异常现象.在4.2K—200K的温度范围内测量了DyMn2Ge2的交流磁化率.在交换相互作用的分子场模型近似下,从理论上分析讨论了DyMn2Ge2的低温自发磁相变和场诱导的磁相变.计算了DyMn2Ge2单晶的磁化强度与温度的变化关系以及不同温度下外磁场沿晶轴c方向时的磁化曲线.理论分析和计算结果表明,温度低于33K时在DyMn2Ge2中观察到的场诱导的一级磁相变为由亚铁磁状态(Fi)到中间态(IS)相变.
关键词:
稀土-过渡族金属间化合物
磁结构
磁相变 相似文献
9.
10.
LuTaO4是最高密度的闪烁体基质, 研究它的结构及其相变对单晶制备具有指导意义. 用固相法制备了Lu2O3和Ta2O5摩尔比为1:1时在不同温度下形成的多晶粉末, 用X射线衍射及Rietveld全谱拟合研究了多晶粉末的物相和结构. 结果表明, Lu2O3: Ta2O5摩尔比为1:1的样品在1740 ℃时合成的物相为M'-LuTaO4, 在1800 ℃时为M'-LuTaO4和M-LuTaO4的混合物, 在1840 ℃时全部转变为M-LuTaO4. 当温度升高到2058 ℃时, 样品呈熔融状态, 对淬火得到的样品进行结构精修, 给出了M-LuTaO4, Lu3TaO7和Ta2O5的晶胞和原子坐标参数, 它们的重量比分别占78.1%, 18.9%和3.0%. 这些结果为制备以LuTaO4为基质的高密度闪烁体单晶具有参考价值.
关键词:
4')" href="#">LuTaO4
相变
粉末衍射
Rietveld精修 相似文献
11.
S. V. Mel’nikova A. S. Krylov A. L. Zhogal’ N. M. Laptash 《Physics of the Solid State》2009,51(4):817-822
Polarization-optical study of twinning and measurements of the Raman spectra and birefringence in oxyfluoride (NH4)3Ti(O2)F5 were carried out over the temperature range 90–350 K. Phase transitions were detected at temperatures T 01 = 266 K (second-order transition) and T 02 = 225 K (first order). It is assumed that the crystal symmetry is changed as follows: Fm3m ? I4/mmm ? I4/m. Anomalies of the spectral parameters are established in the frequency range of internal vibrations of ammonium ions and Ti(O2)F5 complexes. An analysis of the results shows that the transition at T 01 is likely due to small shifts of the tetrahedral groups from their position on the triad axis and that the transition at T 02 is due to fluorine-oxygen ordering of Ti(O2)F5 complexes. 相似文献
12.
E. D. Mishina A. I. Morozov A. S. Sigov N. E. Sherstyuk O. A. Aktsipetrov V. V. Lemanov Th. Rasing 《Journal of Experimental and Theoretical Physics》2002,94(3):552-567
The surface phase transition in a SrTiO3 crystal was studied by second optical harmonic generation. Nonlinear optical response singularities were observed at temperature T*=145 K, which was 40 K higher than the Tc structural phase transition temperature in the crystal volume. Nonlinear critical opalescence in the crystal volume caused by the presence of point defects was studied. The second harmonic field and the intensity of critical opalescence were calculated based on the phenomenological model of nonlinear optical processes with the use of the Landau theory of phase transitions. 相似文献
13.
S. V. Mel’nikova L. I. Isaenko V. M. Pashkov I. V. Pevnev 《Physics of the Solid State》2005,47(2):332-336
Crystals of the KPb2Br5compound are investigated using polarized light microscopy and calorimetry. The birefringence and the angle of rotation of the optical indicatrix are measured in the temperature range 270–620 K. It is found that the KPb2Br5 crystal undergoes a first-order ferroelastic phase transition at temperatures T0↑ = 519.5 K and T0↓ = 518.5 K with a change in the enthalpy ΔH = 1300 ± 200 J/mol. This transition is accompanied by both twinning and the symmetry change mmm ? P21/c. It is revealed that the angle of rotation of the optical indicatrix exhibits an unusual behavior under variations in the temperature due to a strong temperature dependence of the birefringence. 相似文献
14.
Mehmet Erta? Bayram DevirenMustafa Keskin 《Journal of magnetism and magnetic materials》2012,324(5):704-710
The dynamic phase transitions are studied in the kinetic spin-2 Blume-Capel model under a time-dependent oscillating magnetic field using the effective-field theory with correlations. The effective-field dynamic equation for the average magnetization is derived by employing the Glauber transition rates and the phases in the system are obtained by solving this dynamic equation. The nature (first- or second-order) of the dynamic phase transition is characterized by investigating the thermal behavior of the dynamic magnetization and the dynamic phase transition temperatures are obtained. The dynamic phase diagrams are constructed in the reduced temperature and magnetic field amplitude plane and are of seven fundamental types. Phase diagrams contain the paramagnetic (P), ferromagnetic-2 (F2) and three coexistence or mixed phase regions, namely the F2+P, F1+P and F2+F1+P, which strongly depend on the crystal-field interaction (D) parameter. The system also exhibits the dynamic tricritical behavior. 相似文献
15.
U. V. Valiev J. B. Gruber Sh. A. Rakhimov I. S. Edel’man 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(10):1386-1388
Polarized spectra of the optical absorption of the 4f → 4f transition 7
F
6 → 5
D
4 in rare-earth orthoaluminate TbAlO3 were experimentally studied at temperature T = 78 K. It was shown that the nontrivial character of the absorption anisotropy of TbAlO3 at low temperatures could be related either to the symmetry of wave functions of the Stark sublevels of 7
F
6 and 5
D
4 multiplets combining in the optical transitions under study or to optical experiment geometry that takes into account the
orientation of incident light polarization relative to the crystal axes and the axes of local coordinate systems of a rare-earth
ion in orthoaluminate. 相似文献
16.
A sequence of phase transitions in the [(CH3)2NH2]5Cd3Cl11 (DMACC) crystal has been verified based on the study of temperature dependences of the optical birefringence and the data of piezooptical investigations. Absorption spectra in the visible and near-UV regions and IR reflection spectra in the 200–2000-cm–1 region have been obtained. Phase transitions at temperatures of 179.5, 151, and 120 K have been detected. For all the phases of the DMACC crystal, the optical absorption edge obeys Urbach's empirical rule. It is shown that the phonons corresponding to the internal vibrations of the (Cd3Cl11)5– polyhedron participate in the edge formation. 相似文献
17.
I. N. Flerov M. V. Gorev V. D. Fokina A. F. Bovina M. S. Molokeev E. I. Pogorel’tsev N. M. Laptash 《Physics of the Solid State》2007,49(1):141-147
Thermophysical and structural studies of an (NH4)2KMoO3F3 crystal show that this crystal belongs to the family of elpasolites (space group \(Fm\bar 3m\)) and undergoes an order-disorder phase transition at T 0 = 241.5 K. Under hydrostatic pressure, this phase transition splits into two consecutive transitions at the tricritical point with parameters T tr = 232.5 K and p tr=0.21 GPa. It was found that anomalous hysteresis and relaxation phenomena accompany the transitions from the cubic to both distorted phases. The results are analyzed taking into account the data on the phase transition in the related elpasolite (NH4)2KWO3F3. 相似文献
18.
The temperatures at which the cooperative Jahn-Teller phase transitions occur in TbcGd1?cVO4 have been determined from Raman and optical birefringence measurements. Over a narrow range of c there are two transition temperatures; between these temperatures the crystal is distorted, but a higher and lower temperatures the crystal has the same undistorted structure. This unusual behaviour was predicted earlier, and is accurately described by molecular field theory. 相似文献
19.
Phase transitions in the two-dimensional crystalline films adsorbed onto an imperfect substrate (with impurities and defects) are analyzed. It is shown that the phase transition from the commensurate long-range-order (LRO) crystal to the glass state occurs with increase of impurity concentration. The orientational correlation function is shown to tend algebraically to zero at large distances in the glass state. The influence of defects on the phase transition from the LRO-commensurate crystal to the disordered state at the definite temperature Tm is considered. 相似文献
20.
The ferroelectric/ferroelastic phase transition of K2ZnCl4 at 145 K has been investigated employing the tilter method (Kaminsky and Glazer (1996) Ferroelectrics 183, 133) which was adapted to low-temperature experiments. We were able to observe the anisotropy of optical rotation in K2ZnCl4 which shows a distinct discontinuity at the transition temperature. A precursor-optical rotation in the ferroelectric phase is discussed in connection with a cluster ordering scheme suggested in an earlier X-ray study. The rotation of the optical indicatrix which accompanies the transition from the orthorhombic to the monoclinic system shows a Landau-type temperature dependence. Model calculations based on the dipole-dipole interaction between the atoms of the structures at different temperatures are in qualitative agreement with the experimental results. 相似文献