共查询到20条相似文献,搜索用时 156 毫秒
1.
2.
高压下的电学性质测量是获得材料物理性质的有效手段。利用集成在金刚石对顶砧上的薄膜微电路,测量了高压下Fe3O4/β-CD(β-糊精)的电导率,并分析了电导率随压力的变化关系。在0~39.9 GPa范围内,Fe3O4/β-CD的电导率随压力的增加而逐渐增大,并呈半导体的特征;而在17.0 GPa处其电导率发生突变,表明样品发生了高压相变。在卸压过程中,电导率随压力的变化呈线性关系,并且卸压后样品的电导率不能回到最初的状态,推测这是一个不可逆的高压结构相变。 相似文献
3.
4.
5.
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
6.
采用平面波赝势方法对菱铁矿FeCO3高压下的晶体结构, 电子构型和电子结构进行了第一性原理计算研究. 研究过程中考虑了菱铁矿FeCO3真实的反铁磁(AFM) 自旋有序态, 模拟静水压环境, 从零压逐步加压到500 GPa. 在40---50 GPa压力范围内, FeCO3发生了从高自旋(HS) AFM态到低自旋(LS) 非磁性(NM) 态的磁性相变, 伴随着晶胞体积坍塌10.5%. FeCO3在相变前后均是绝缘体, 但是相变后的LS-NM态的Fe2+ 离子的3d电子局域化程度更强, 能隙随着压力的进一步增大而逐步增大, 离化程度更高, 直到500 GPa没有发生金属绝缘体相变. 相似文献
7.
8.
为了合成出理论预言的具有致密结构的超硬材料C3N4,运用二级轻气炮加载和冲击回收实验技术,以富含N的g-C3N4为前驱物,在40~65 GPa压力下完成了冲击合成实验。在低于51 GPa压力时,X射线衍射分析表明,在回收样品中未发现有新相生成,说明g-C3N4是稳定的;而在51~65 GPa范围内,回收样品中有新相生成,与理论计算结果对照发现,新相为β-C3N4相,且不含其它结晶相。证实利用冲击合成方法将g-C3N4直接转化为单纯β-C3N4是可能的,对纯净的超硬相碳氮化合物的合成研究具有参考意义。 相似文献
9.
10.
采用金刚石压砧高压装置,研究了双钙态矿结构化合物Sr2FeNbO6及其掺杂物Sr2FeMo0.3Nb0.7O6在室温下,20 GPa内电阻和电容随压力的变化,并发现Sr2FeNbO6在7.5 GPa左右压力下发生了相变,而Sr2FeMo0.3Nb0.7O6的相变发生在2.8 GPa左右。并结合这两个样品的高压下的同步辐射能散X射线衍射实验,进一步证明了这两种相变是电子结构相变引起的。 相似文献
11.
在活塞圆筒式p-V关系测量装置上,研究了KH2PO4(KDP)和(CH3NHCH2COOH)CaCl2[Tris-sarcosine calcium chloride(TSCC)]在室温下、4.5 GPa内的p-V关系。实验结果表明:KDP在2.1 GPa左右有一个相变;TSCC在0.8 GPa和3.2 GPa左右各有一个相变。本工作还给出了它们在相变前后的状态方程,以及它们的格临爱森参数γ0、体积模量B0和B0的压力导数B0'。 相似文献
12.
Payal Baid Rampuria Nisha Yadav Usha Chandra N. V. Chandra Shekar P. Ch. Sahu 《Hyperfine Interactions》2008,184(1-3):91-96
Pressure-induced structural changes on nano-crystalline La0.8Sr0.2Mn0.8Fe0.2O3 were studied using high-pressure Mössbauer spectroscopy and high-pressure X-ray diffraction. Mössbauer measurements up to 10 GPa showed first order transition at 0.52 GPa indicating transformation of Fe4?+? to high spin Fe3?+?, followed by another subtle transition at 3.7 GPa due to the convergence of two different configurations of Fe into one. High-pressure X-ray diffraction measurements carried up to 4.3 GPa showed similar results at 0.6 GPa as well as 3.6 GPa. Attempts were made to explain the changes at 0.6 GPa by reorientation of grain/grain boundaries due to uniaxial stress generated on the application of pressure. Similarly variation at 3.6 GPa can be explained by orthorhombic to monoclinic transition. 相似文献
13.
Nanocomposite of hard (BaFe12O19)/soft ferrite (Ni0.8Zn0.2Fe2O4) have been prepared by the sol–gel process. The nanocomposite ferrite are formed when the calcining temperature is above 800 °C. It is found that the magnetic properties strongly depend on the presintering treatment and calcining temperature. The “bee waist” type hysteresis loops for samples disappear when the presintering temperature is 400 °C and the calcination temperature reaches 1100 °C owing to the exchange-coupling interaction. The remanence of BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite with the mass ratio of 5:1 is higher than a single phase ferrite. The specific saturation magnetization, remanence magnetization and coercivity are 63 emu/g, 36 emu/g and 2750 G, respectively. The exchange-coupling interaction in the BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite is discussed. 相似文献
14.
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
15.
The structural, electronic and thermodynamic properties of cubic Zn3N2 under hydrostatic pressure up to 80 GPa are investigated using the local density approximation method with pseudopotentials of the ab initio norm-conserving full separable Troullier-Martin scheme in the frame of density functional theory. The structural parameters obtained at ambient pressure are in agreement with experimental data and other theoretical results. The change of bond lengths of two different types of Zn-N bond with pressure suggests that the tetrahedral Zn-N bond is slightly less compressible than the octahedral bond. By fitting the calculated band gap, the first and second order pressure coefficients for the direct band gap ofthe Zn3N2 were determined to be 1.18×10−2 eV/GPa and −2.4×10−4 eV/(GPa)2, respectively. Based on the Mulliken population analysis, Zn3N2 was found to have a higher covalent character with increasing pressure. As temperature increases, heat capacity, enthalpy, product of temperature and entropy increase, whereas the Debye temperature and free energy decrease. The present study leads to a better understanding of how Zn3N2 materials respond to compression. 相似文献
16.
In our previous study, Mn-substituted nickel hydroxide (Ni0.8Mn0.2(OH)2) was prepared by a simple ball milling method to reduce the cost of nickel hydroxide for alkaline secondary battery, but compared to the Ni(OH)2 electrode, the Ni0.8Mn0.2(OH)2 one showed an obvious decrease in its discharge potential. In this paper, Zn and Mn co-substituted nickel hydroxide (Ni0.8Mn0.2???x Zn x (OH)2, x?=?0–0.075) is prepared by ball milling. The results of the cyclic voltammetry (CV) tests illustrate that the co-reduction of Mn(IV) to Mn(III) and NiOOH is observed on the Ni0.8Mn0.2???x Zn x (OH)2 electrodes, and it has a lower reduction potential than NiOOH. The co-substitution of Zn can effectively increase the co-reduction potential. The ball-milled Ni0.8Mn0.15Zn0.05(OH)2 electrode has a similar capacity (about 270 mAh g?1 at a 0.2C rate) and cycling durability to the commercial Ni(OH)2 with ball milling treatment, but the former has better high-power performance. 相似文献
17.
The electronic structure and magnetic properties of Ni2MnB upon pressure up to 20 GPa have been studied by using the density functional theory (DFT) method. The results indicate that ferromagnetic ordered Ni2MnB in L21 structure is more stable than the nonmagnetic one. The magnetic moments of Ni and Mn atoms as well as the total magnetic moment of Ni2MnB are found to decrease weakly with increasing pressure. The pressure derivative of the total magnetic moment is −3.07×10−3 GPa−1. The equilibrium bulk modulus and its derivative from the Murnaghan equation of state (EOS) are B0=247.7 GPa, B′=4.98. 相似文献
18.
Fe50Ni37Mn13, which is a ferromagnetic alloy with FCC crystal structure, has been reported to show the Invar effect below the Curie temperature; however, this alloy shows a typical anti-Invar effect above the Curie temperature. In this paper, we discuss the pressure dependence of the temperature variation of the alternative current (AC) susceptibility at a frequency of 1 kHz for Fe50Ni37Mn13 at various pressures up to 7.5 GPa above 77 K; we then compare the results with those for Fe68.1Ni31.9, which were obtained in a previous study. Fe50Ni37Mn13 was in a ferromagnetic state throughout the entire pressure range measured. TC decreases in inverse proportion to the increasing pressure; dTC/dp and dln TC/dp for Fe50Ni37Mn13 are −26 K GPa−1 and −0.07 GPa−1, respectively. Further, the temperature variation of the shape of the χ′-T curve for different pressures indicates continuous combining of magnetic interactions occurs at high pressures. These results are similar to those obtained for Fe68.1Ni31.9. 相似文献
19.
O. Mounkachi A. Benyoussef A. El Kenz E.H. Saidi E.K. Hlil 《Journal of magnetism and magnetic materials》2008
Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA), we investigated the magnetic and half-metallic properties of Mn-doped p-type ZnO and the mechanism which control these properties. Mn-doped ZnO is anti-ferromagnetic spin-glass state, but it becomes half-metallic ferromagnetic upon holes doping. The electronic structure, total magnetic moment of Zn0.8Mn0.2O1−yNy and magnetic moments of Mn and N in Zn0.8Mn0.2O1−yNy are calculated for different holes (y) concentrations. In this paper we address the origin of half-metallic and ferromagnetic properties as controlled and oriented by the nature of hybridization of the Mn (3d) state and host p(N) states. The band structure has been used to explain the strong ferromagnetism observed in Zn0.8Mn0.2O0.1N0.9. 相似文献
20.
Spinel LiMn2O4 and LiMn1.4Cr0.2Ni0.4O4 cathode materials were successfully synthesized by the citric-acid-assisted sol-gel method with ultrasonic irradiation stirring. The structure and electrochemical performance of the as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometer, cyclic voltamogram (CV) and the galvanostatic charge-discharge test in detail. XRD shows that all the samples have high phase purity, and the powders are well crystallized. SEM exhibits that LiMn1.4Cr0.2Ni0.4O4 has more uniform cubic-structure morphology than that of LiMn2O4. EDX reveals that a small amount of Mn3+ still exists in LiMn1.4Cr0.2Ni0.4O4. The galvanostatic charge-discharge test indicates that the initial discharge capacities for the LiMn1.4Cr0.2Ni0.4O4 and LiMn2O4 at 0.15 C discharge rates are 130.8 and 130.2 mAh g−1, respectively. After 50 cycles, their capacity are 94.1% and 85.1%, respectively. The CV curve implies that Ni and Cr dual substitutions are beneficial to the reversible intercalation and deintercalation of Li+, and suppress Mn3+ generation at high temperatures and provide improved structural stability. 相似文献