Communications in Theoretical Physics
The mistakes in Ref. [3] are pointed out. Some important problems are discussed, and the correct ideas, calculations and results are given. The R-line thermal shift of MgO:V2+ at normal pressure is the algebraic sum of the contribution from electron-phonon interaction and the contribution from thermal expansion. The latter can be calculated by using the thermal expansion coefficient and the pressure-induced shift.
关键词:
R-line thermal shift of MgO : V2+;pressure;temperature
Communications in Theoretical Physics
A great improvement on a previous work (Phys, Rev. B48 (1993) 14067) has been made. By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d(3) electronic configuration, the values of all the parameters in the expressions of thermal shift (TS) and thermal broadening (TB) from EPI for the ground level, R level and R line of MgO:V2+ have microscopically been evaluated; and then, both the TS and TB of R line and various contributions to them have uniformly been calculated. The results are in very good agreement with the experimental data. It is found that all the three terms of TS from EPI are red shifts; the term of the contribution to TS from thermal expansion is blue shift. The Raman term is the largest, and the other terms are also important for TS. The R-line TS of MgO:V2+ comes from the first-order term of EPI. The elastic Raman scattering of acoustic phonons plays a dominant role in R-line TB of MgO:V2+. For calculations of both the TS and TB, it is very important to take into account all the admixtures of wavefunctions.
关键词:
crystal fields;optical properties;electron-phonon interaction;electronic structure;thermal shift and broadening;thermal expansion;pressure-induced shifts;energy-spectrum;sharp lines;ruby;temperature;mgo;v2+
Journal of Physics-Condensed Matter
Using x-ray diffraction, powder neutron diffraction, high-field magnetization measurement and thermomagnetic analysis, we have studied the structural and magnetic properties of RFe(10)V(2)C(0.5) alloys (R = Sm or Y) made by are melting, in which the carbon was added using Fe-C alloy. Both samples are found to be nearly single phase with ThMn12-type structure and with a small amount of alpha-Fe phase (less than 4 wt%). The neutron diffraction of the Y-containing compound indicates that the real composition of the main phase is Y(Fe9.87V1.90C0.23)C-0.27. and that the carbon atoms occupy not only the interstitial 2b site but also the substitutional 8i site. The Fe moments of the 8i site as well as the 8j site are found to be reduced in the Y(Fe9.87V1.90C0.27)C-0.27 compound compared with its carbon-free counterpart. The decrease in the Fe moment at the 8j site is due to the surrounding interstitial carbon atoms, while the decrease in the Fe moment at the 8i site is ascribed to the surrounding substitutional carbon atoms as nearest neighbours. The high-field magnetization measurements indicate that the anistropy held of SmFe10V2C0.5 and YFe10V2C0.5 are slightly higher than those of SmFe10V2 and YFe10V2, respectively. In SmFe10V2C0.5, the magnetization curve in the hard direction at 4.2 K shows a first-order-magnetization-process (FOMP)-like or quasi-FOMP-like transition.
关键词:
intermetallics;y(fe11ti);nitride;metal;gd;tm;c)
张少鸿
,
付娟
,
苏秋成
,
吴梁鹏
,
李新军
稀有金属
以草酸和V2O5为原料,采用水热法制备VO2(B).通过高温原位X射线衍射技术研究VO2(B)在氮气保护下升高温度过程中的相变特性,采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)和激光拉曼光谱技术分析所制备样品及其在不同温度热相变产物的微观形貌、晶体结构和物相组成.结果表明:以草酸和V2O5为原料,用水热法可制得单斜晶系VO2(B),颗粒呈纳米片状;升温至430～700℃之间,VO2(B)不可逆转化为四方晶系VO2(R),形貌由纳米片状变为亚微米及微米近球形;升温至1000℃左右,VO2(R)开始分解形成Magnéli相系列化合物(VnO2n-1,3≤n≤9);升温至约1200℃完全转变为具有刚玉结构的V2O3烧结块.
关键词:
水热法
,
氧化钒
,
原位XRD
,
热相变
,
拉曼光谱
Journal of Solid State Chemistry
The subsolidus phase relations of R2O3-CaO-CuO ternary systems (R = Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950degrees in air. There exists a ternary compound Ca14-xRxCu24O41 (x = 4 for R = Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca2+xR2-xCu5O10 (R = Nd, Sm, Gd, Tm) with a wide composition range Deltax of about 0.6. The compound Ca14-xRxCu24O41 possesses a layered orthorhombic structure and is isostructural to Sr14-xCaxCu24O41. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca2+xR2-xCu5O10 solid solution is isostructural to Ca2+xY2-xCu5O10, the structure of which is based on an orthorhombic "NaCuO2-type" subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels. (C) 2002 Elsevier Science (USA). All rights reserved.
关键词:
R2O3-CaO-CuO (R = Nd, Sm, Gd, Tm) systems;phase relations;Ca10R4Cu24O41 (R = Nd, Sm, Gd) structure;Ca2+xR2-xCu5O10 (R = Nd, Sm,;Gd, Tm) structure;ternary-system;approximately 950-degrees-c;high-pressure;superconductivity;diagram;air;er;compatibilities;property;oxide
Physica B-Condensed Matter
X-ray powder diffraction and magnetization measurements reveal that light rare earth and heavy rare earth have different effects on the structure, Curie temperature and magnetic phase transition of the compounds R(Co1-xGax)(2) (R = Nd, Gd, Tb, Dy) (x = 0.0-0.3). The lattice constant exhibits a giant increase with increasing Ga concentration in all compounds. The Curie temperature shows no variation for R = Nd, a monotonic decrease for R = Gd and a maximum for R=Tb and Dy, respectively. The Curie temperature is strongly related with volume expansion, in which a critical value of a(c) approximate to 7.26 Angstrom is reached. The observed magnetic transition in all compounds is well explained within the framework of the Inoue-Shimizu model. It is revealed that both the lattice constant and the Curie temperature have a strong relationship with the order of the magnetic phase transition. (C) 2003 Elsevier B.V. All rights reserved.
关键词:
structure;Curie temperature;magnetic phase transition;itinerant-electron metamagnetism;intermetallic compounds;ac;susceptibility;order;temperature;behavior;r(co;yco2
Communications in Theoretical Physics
The unified theoretical calculation of thermal shifts (TS) of R-1 and R-2 lines and thermal broadenings (TB) of R, R' and B lines for ruby was carried out for the first time. The calculated results are in very good agreement with a great number of experimental data. Especially by using quantum theory and taking into account all the admixtures of wavefunctions within d(3) electronic configuration, all the Gamma M in electron-phonon interaction (EPI), the electronic energy spectrum and lattice-vibration Spectrum, the very important contributions to TS and TB from single-phonon direct process were theoretically calculated in detail. The microscopic essentials of various contributions are revealed, and the mistakes in previous work are remedied.
关键词:
diamond anvil cell;pressure measurement;spectroscopy;temperatures
Journal of Magnetism and Magnetic Materials
High-field free-powder (HFFP) magnetization measurements were performed at 4.2 K on R6Fe13Sn (R = Nd, Pr). A metamagnetic first-order transition at 8-10 T accompanied by a large hysteresis is found in the HFFP magnetization curve of Nd6Fe13Sn. By means of X-ray diffraction on magnetically aligned samples, the easy magnetization directions at room temperature were found parallel to the c-axis for Pr6Fe13Sn, and perpendicular to the c-axis for Nd6Fe13Sn. A peaked section in the low-temperature range, corresponding to a canted configuration of the moments of the magnetic sublattices, was traced in the thermomagnetic curve of a free-powder sample of Pr6Fe13Sn. The magnetic-ordering temperatures of Pr6Fe13Sn and Nd6Fe13Sn are 396 and 374 K, respectively. (C) 1998 Elsevier Science B.V. All rights reserved.
关键词:
rare-earth intermetallics;coercivity;crystal-structure
