交换作用对 CeF3晶体磁性和磁光效应的影响

研究了顺磁性晶体CeF3内交换作用有效场随温度的变化关系,给出了其形式为Hin=(-0.68-0.002T)×10-6M.结合该关系,用量子理论的计算得到了与实验值吻合较好的磁化率倒数、Verdet常数倒数随温度的变化关系,并且用光磁效应的概念和规律对结果作了进一步分析,指出光诱导促进了该晶体内电子间的交换作用.     

晶场二级效应与交换作用对PrF3晶体磁性及磁光性质的影响

研究了晶场二级效应在PrF₃晶体中的作用，发现该效应可使Pr³⁺离子的晶场单态与其他态混合，对PrF₃晶体磁化率产生明显影响.进一步研究了晶体内的交换作用有效场，其形式为H_in=(1.9-0.02556T)×10^-5M，在100—300 K的温度范围内，以此计算的PrF₃晶体的倒数磁化率和Verdet常数的倒数与实验值符合较好.结果表明，在PrF₃晶体中，晶场二级效应与离子间的交换作用都不能忽略. 关键词： 晶场二级效应 交换作用有效场 Verdet常数 3晶体')" href="#">PrF₃晶体     

PrNi$lt;sub$gt;2$lt;/sub$gt;的磁和磁热性能研究

在一些磁性材料内, 磁性离子间交换作用和磁性离子的自旋涨落对材料磁性有影响. 本文根据磁比热实验值确定了晶场参数后, 利用包含自旋涨落的交换作用有效场H_m= n₀ (1 + γ T + β e^{ω T})M, 计算了PrNi₂晶体晶场能级的Zeeman劈裂. 在温度为3.8 K ≤T≤ 30 K范围内, 计算了该晶体多晶磁矩随外磁场的变化, 以及外磁场H=5000 Oe时磁化率倒数随温度的变化, 计算结果和实验值符合较好. 当外磁场在0–50000 Oe时, 计算的该晶体的磁熵变与已有文献的理论结果相似. 计算结果说明, 提出的包含自旋涨落的交换作用有效场不仅适合亚铁磁性晶体, 而且也适合顺磁性晶体. 关键词： 2')" href="#">PrNi₂ 磁比热 交换作用有效场 磁矩 磁熵变     

晶场二级效应与交换作用对PrF3晶体磁性及磁光性质的影响

研究了晶场二级效应在PrF3晶体中的作用,发现该效应可使Pr3+离子的晶场单态与其他态混合,对PrF3晶体磁化率产生明显影响.进一步研究了晶体内的交换作用有效场,其形式为Hin(1.9-0.02556T)×10-5M,在100-300 K 的温度范围内,以此计算的PrF3晶体的倒数磁化率和Verdet常数的倒数与实验值符合较好.结果表明,在PrF3晶体中,晶场二级效应与离子间的交换作用都不能忽略.     

Dy3Al5O12磁热性质研究

用量子理论计算了Dy₃Al₅O₁₂的晶场能谱、Zeeman劈裂能级和波函数. 在外磁场H_e为0<H_e<9 T, 温度为3<T<42 K 范围内, 计算了该晶体的磁矩、磁熵变, 计算结果与相关实验数据吻合较好. 该计算结果表明, Dy₃Al₅O₁₂内磁性离子间的交换作用非常微弱, 可以忽略. 从理论上给出了绝热退磁过程中温度变化ΔT与T的关系, 并与Gd₃Ga₅O₁₂晶体进行了比较, 发现不同外磁场下, Dy₃Al₅O₁₂和Gd₃Ga₅O₁₂的低温制冷性能在不同温区有差别. 在进行低温(T<10 K)制冷时, 若外磁场较低, 选择Dy₃Al₅O₁₂作为磁制冷材料较好; 若外磁场较高, 选择Gd₃Ga₅O₁₂作为磁制冷材料较好.     

高温条件下Ga3PO7晶体热学及声表面波性质的理论研究

高温压电晶体是许多机电器件必需的一种多功能材料, Ga₃PO₇晶体的居里温度高达1364 ℃, 可应用于高温极限条件. 但是预测高温极限条件下晶体的结构以及物理性质的问题采用实验研究的手段非常困难, 而理论上的预测未见研究. 本文采用密度泛函-准谐振近似理论计算了温度在0-1200 ℃范围内Ga₃PO₇ 晶体的结构常数和热学性质, 结果表明Ga₃PO₇晶体的晶格常数a和c随温度的升高呈线性增大, 且c方向受温度影响更为显著; 晶体的密度随温度的升高而减小, 计算的a 和c方向平均热膨胀系数分别为1.67×10^-6 K^-1和3.58×10^-6 K^-1, 高温区定压热容为2.067 J/g·K, 与实验值一致. 计算了从常温到高温下该晶体的弹性常数以及体弹性模量的变化, 研究了高温条件下的声表面波特性, 发现随着温度的升高, 声表面波速度浮动较小, 而机电耦合系数略有增大; 在传播角为151° 时该晶体具有较好的温度稳定性且机电耦合系数达到最大值, 这表明Ga₃PO₇ 晶体是一种有望应用于高温环境下的压电晶体.     

LiB3O5晶体高温拉曼光谱研究

研究了LiB₃O₅晶体在不同温度下(在300—1173K的温度范围)的拉曼光谱,分析了LBO晶体结构随温度变化的规律.随着温度的升高,LBO晶体的拉曼光谱谱峰都不同程度地向低波数方向移动,也存在不同程度的展宽,同时强度减弱.发现晶体在1100K存在明显相变,与LBO晶体的相图给出的1107K的相变温度基本相符. 关键词： 3O₅晶体')" href="#">LiB₃O₅晶体 高温拉曼光谱 相变     

由BaTiO3晶体结构相变时的介电特性研究其电场作用下的偶极子偏转路径

在不同频率和偏置电场下测量了BaTiO₃晶体从三方相到正交相再到四方相相变过程中的介电温谱.基于BaTiO₃晶体在电场作用下的偶极子偏转假设和介电特性实验结果,提出BaTiO₃各结构相在电场作用下的偶极子偏转路径可以由其相邻相的介电常数随温度的变化特性表现出来.推断出各结构相的偶极子偏转路径,以及偏置电场对偶极子偏转路径的影响. 关键词： 3晶体')" href="#">BaTiO₃晶体 介电特性 结构相变 偶极子偏转路径     

BiFeO3/Ni81Fe19磁性双层膜中的交换偏置及其热稳定性研究

研究了磁场诱导生长的BiFeO₃/Ni₁₈Fe₁₉磁性双层膜中 的交换偏置及其热稳定性. 结果表明: BiFeO₃/Ni₁₈Fe₁₉双层膜中的交换偏置场H_ex未表现出明显的磁练习效应. 在负饱和磁场等待过程中, BiFeO₃/Ni₁₈Fe₁₉双层膜磁滞回线的前支和后支曲 线都随着在负饱和磁场中等待时间t_sat的增加向正场方向偏移. 交换偏置场H_ex的大小随着等待时间t_sat的增加而减小, 矫顽力H_c基本不变. 交换偏置场H_ex的大小随测量温度T_m的升高变化不明显, 表现出良好的热稳定性; 但矫顽力H_c随T_m的升高而显著减小. 良好的热稳定性应该来源于铁电性和反铁磁性间的共同耦合作用. 关键词： 多铁性 磁性薄膜 交换偏置 热稳定性     

Pr3+在SBN晶体中的发光特性

通过测量Ｐｒ：ＳＢＮ晶体的吸收光谱和荧光光谱来确定Ｐｒ³⁺在ＳＢＮ晶体中的能级位置。由于Ｐｒ³⁺离子占据晶体中的不同格位而引起荧光带呈现双峰结构。测量荧光寿命随温度的变化关系，表明Ｐｒ³⁺在ＳＢＮ晶体中 ³Ｐ₀态的无辐射弛豫主要是 ³Ｐ₀→¹Ｄ₂多声子弛豫过程。 关键词：     

Improvement to the exchange field acting upon Tb ions in TbIG

The spin fluctuations of the magnetic ions play an important role on the magnetic properties of the crystals and lead to a new mechanism for the Curie-Weiss susceptibility. The exchange field H_exch acting on the rare-earth ions in Tb:YIG is improved based on the temperature dependence of the spin fluctuations, which is expressed as H_exch=n₀(1+γT+βT⁻²)M_YIG. By means of the improved exchange field, the magnetic and magneto-optical properties of Tb³⁺ ions in Tb:YIG are calculated. The calculated results are in good agreement with the measured data in the temperature range from 40 to 300 K.     

EPR of Gd3+ - doped CeF3 single crystal: Linewidth variation with temperature

Detailed X-band EPR study of a Gd³⁺-doped CeF₃ single crystal has been made from 4.2 to 473 K, with particular attention to EPR linewidths. In general, it is found that there are four regions over which the log-log plot of the linewidth versus temperature is linear, implying separate power-law dependences of the linewidth. Gd³⁺ spin Hamiltonian parameters in CeF₃ have been estimated at various temperatures from the line positions. From the linewidth variation with temperature the Debye temperature has determined to be about 140 K.     

Analysis of inelastic scattering processes of electrons by localized electrons in quantum dots

The inelastic Coulomb scattering rate 1/τ_in of conduction electrons has been theoretically evaluated in the presence of localized states such as quantum dots. By a diagrammatical method, we have formulated 1/τ_in and its relation to the conductivity σ_loc(ω) through localized states. The dependence of τ_in on temperature T is examined in the case that σ_loc(ω) follows the Mott's model. It is found that 1/τ_in varies as T²(ln Δ/T)^d+1 where d is the dimensionality and Δ is tunneling energy between the localized states in the asymptonic T = 0 limit, in agreement with Imry's calculation. It is also found that calculated 1/τ_in deviates from T²(ln Δ/T)^d+1 as T increases, suggesting the importance of correction term at high temperature.     

High pressure 17O NMR study of solvent exchange on square planar complexes: Water exchange on [Pd(dien)H2O]2+

Abstract

The water exchange reaction of [Pd(dien)H₂O]²⁺ (dien = diethylenetriamine) was studied as function of temperature (268-308 K) and pressure 0.1-197 MPa) using ₁₇O NMR techniques. The rate and activation parameters are: k_cx = 5100 s^?1 at 298 K; ΔH^# =38 kJ mol^?1; ΔS^# = -47 JK^?1 mol^?1; ΔV^# = -2.8 cm³ mol^?1 at 296 K. The results are discussed in reference to solvent exchange data for other Pt(II) and Pd(II) complexes, and are interpreted in terms of an associatively activated substitution process.     

Ion exchange kinetics of polycrystalline Na/Kβ/β″-Al2O3

The ion exchange kinetics of polycrystalline Na/K β/β″-Al₂O₃ soaked in H₂SO₄ were studied. The rate of ion exchange in hot concentrated H₂SO₄ was determined by monitoring the change of solution alkali content. The H₃O⁺ diffusion coefficient was estimated from the resulting time dependence data and the ceramic conductivity calculated. Dilute H₂SO₄ with a constant applied voltage was also studied and the ceramic conductivity calculated from the change of current with time. The estimated conductivities obtained by the two methods are compared with reported values for H₃O⁺-β- and β″-Al₂O₃ single crystals. Utilising an H₃O⁺ jump model, the estimated values reflect intragranular conduction.     

Photoluminescent properties of CeF3:Tb3+ nanodiskettes prepared by hydrothermal microemulsion

In this paper, CeF₃:Tb³⁺ nanodiskettes were prepared by the hydrothermal microemulsion method for the first time and the photoluminescent properties of CeF₃:Tb³⁺ nanodiskettes were investigated. The structural properties of CeF₃:Tb³⁺ nanodiskettes were characterized by X-ray diffractions and transmission electron microscopy. The photoluminescent properties of CeF₃:Tb³⁺ with different Tb³⁺ ions concentration were investigated by excitation spectra, emission spectra and lifetime measurement. The energy transfer processes from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Tb³⁺ were analyzed and discussed. Results show that CeF₃:Tb³⁺ nanodiskettes may be applied as phosphors for high resolution displaying. PACS 78.55; 78.66; 79.60     

Upconversion studies in rare earth ions-doped lanthanide materials

In the present work, results of upconversion emission in various powder samples have been discussed. The powder upconversion phosphors such as La₂O₃:Er³⁺/Yb³⁺, LaF₃:Er³⁺/Yb³⁺, CeO₂:Er³⁺/Yb³⁺, CeF₃:Er³⁺/Yb³⁺ were prepared and their upconversion emission, using 976 nm wavelength excitation, was investigated in depth. These phosphors have shown good upconversion emission in the visible region except for the CeF₃:Er³⁺/Yb³⁺ phosphor. Two intense bands around 525 and 550 nm due to the ² H _11/2 →⁴ I _15/2 and ⁴ S _3/2 →⁴ I _15/2 transitions, respectively, are found to be in a thermally coupled state in these samples. The intensity ratio of these two bands permitted us to estimate the temperature of the environment. The pump power studies of the emission bands of these samples are also made to understand the dynamics of the upconversion emission.     

正庚烷高温裂解的温度敏感性

利用ReaxFF分子动力学模拟方法对正庚烷在高温条件下的热解行为进行了研究．细致分析了温度对正庚烷高温裂解过程以及产物分布的影响．结果显示温度对正庚烷的热解过程的影响是分阶段的．高温能加速正庚烷的分解,但是当温度达到一定阶段之后这种影响逐渐变小．正庚烷的热解可以分为三个阶段．主要产物C₂H₄、C3和C4的质量百分数随转化率的变化规律与实验值符合很好．利用一阶动力学模型得到的正庚烷热解的表观活化能和指前因子分别为53.96 kcal/mol和55.34×10¹³ s^-1,与实验值相符．     

稀磁合金的杂质互作用效应

本文用格林函数方法讨论Tk(Kondo温度)时杂质互作用对Kondo效应的影响。对s-d互作用哈密顿量作自洽场近似时,同时计入导致Kondo效应和产生杂质互作用的切断项,求得了杂质系统的Kondo温度和低温电阻。结果表明:在稀磁合金中,杂质间的互作用效应使Kondo温度下降,并且使T《T_k时的电阻率温度变化曲线由(1-AT²)型变为(1+BT²)型(A,B>0),从而可能在Tk温区产生电阻极大。 关键词：