含红外发散的集团自旋玻璃体系的超声吸收

本文将红外发散响应理论应用到集团自旋玻璃体系中磁集团取向变化弛豫过程,研究自旋玻璃体系(COF_7)_(0.5)(BaF_2)_(0.2)(NaPO_3)_(0.3)的低温超声吸收特性。结果表明T<4.0K时,超声吸收的磁贡献部分主要来自于磁集团的集体转向弛豫过程;T>4.0K时,超声吸收的磁贡献部分是集团集体转向过程和集团内部贡献的迭加。     

石英中Al3+-空穴取向变化弛豫过程中的红外发散响应

基于α石英的晶体结构，将红外发散响应模型和双势阱模型应用到含Ａｌ杂质的α石英中Ａｌ³⁺－空穴的取向变化弛豫过程，研究其低温介电损耗特性，结果表明Ｔ＜６．５Ｋ时，介电损耗的主要贡献来自于单声子助隧道弛豫过程；Ｔ＞１０Ｋ时，主要贡献来自于热跃迁弛豫过程；而在中间温区，介电损耗是两种过程的迭加，同一弛豫体不同的弛豫过程对应于不同的红外发散响应，还讨论了同一弛豫体引起的超声弛豫损耗。 关键词：     

玻璃超声吸收的红外发散理论

本文采用低频涨落、耗散、弛豫过程的统一理论来研究玻璃热活化弛豫过程的超声吸收。与现有的弛豫时间分布理论不同,只采用单一弛豫时间τ_p,但可以说明弛豫时间分布理论所不能解决的玻璃超声吸收的实验特征,并解释这些实验特征与具体材料无关的普适性。 关键词：     

石英中Al~（3＋）－空穴取向变化弛豫过程中的红外发散响应

基于ａ石英的晶体结构，将红外发散响应模型和双势阱模型应用到含Ａｌ杂质的ａ石英中Ａｌ￣（３＋）－空穴的取向变化弛豫过程，研究其低温介电损耗特性，结果表明Ｔ＜６．５Ｋ时，介电损耗的主要贡献来自于单声子助隧道弛豫过程；Ｔ＞１０Ｋ时，主要贡献来自于热跃迁弛豫过程；而在中间温区，介电损耗是两种过程的迭加，同一弛豫体不同的弛豫过程对应于不同的红外发散响应，还讨论了同一弛豫体引起的超声弛豫损耗。     

含红外发散的低温玻璃超声声速理论

本文采用红外发散和隧道态模型,讨论玻璃超声声速在3K温度以下的行为。我们把声速的改变看作两部分组成:无弛豫过程和有弛豫过程。前者采用“玻色型元激发”理论处理;后者采用“含红外发散的隧道弛豫”理论处理。我们不但得到与实验符合较好的声速-温度曲线,并且解释了一般频率下(10⁷Hz,T为0.3—1K),声速与频率无关的lnT规律和高频下(2GHz,T<0.1K)声速存在极小值的现象。 关键词：     

快离子导体玻璃滞弹性弛豫的红外发散响应

本文依据Ngai(倪嘉陵)的低频激发、弛豫、耗散理论和非晶态快离子导体的特点,提出了非晶态快离子导体的滞弹性弛豫理论。认为快离子导体玻璃中的超声吸收主要来源于与玻璃网络呈微弱联系的快离子的热激活弛豫及伴之而来的低能激发的损耗。理论成功地描述了超声吸收的频率、温度依赖关系,解释了弛豫时间分布理论所不能解释的快离子导体玻璃的实验特征。     

海水的低频化学弛豫声吸收

用圆柱共振器法测量了三种混合水溶液的声吸收与pH值的依赖关系,溶液中每种化学成分的浓度均参照Lyman-Fleming人造海水配方中对应成分的浓度来选取。测量的频率为2.9和6.8kHz。温度为12.4℃。结果表明,在海水的pH值范围内,B(OH)_3弛豫的弛豫频率与pH值没有明显依赖关系。另外由实验结果可以看出在B(OH)_3/CO_2/Ca/Mg/NaCl水溶液中还存在一个由MgHCO~+_3引起的低频弛豫,其弛频约为3.5kHz。文末列出了由本文测得的B(OH)_3,MgCO_3和MgHCO~+_3弛豫的弛豫参数。     

锗酸铋晶体的超声特性

本文采用超声脉冲回波法在4.2K—300K温区内测试了锗酸铋晶体[110]和[111]晶向的超声纵波衰减与温度的关系,结果在50K附近均出现由于激活弛豫过程所引起的大的异常衰减峰;本文还用脉冲回波重合法精密测定了[100],[110]和[111]晶向的超声纵波和横波的声速,并由此计算出弹性常数C_(11),C_(44)和C_(12)。     

非晶态快离子导体(AgI)x(Ag4P2O7)1-x的声学性质

用液氮骤冷方法制备了(AgI)_x(Ag₄P₂O₇)_1-x系列非晶态快离子导体。对AgI摩尔浓度x=0.50,0.60,0.67,0.75,0.80的样品,在77—300K温度范围及2,5,10,15MHz的频率上测量了纵波和横波的超声衰减和声速。发现在200—240K附近存在一个异常强的弛豫型超声吸收峰,随AgI含量的增加,该峰的位置向低温方向移动,且峰的高度增大。在实验的温度范围内,观察到纵波和 关键词：     

海水中硼酸弛豫声吸收机理的研究

通过共振器法测量获得了硼酸弛豫的弛豫频率和最大波长吸收与硼酸及碳酸氢钠浓度的依赖关系.实验结果可以用一个表观的一步反应:B(OH)_3+CO~2-_3(总)+H_2O(?)B(OH)~-_4(总)+HCO~-_3(总)来解释。本文的理论和实验表明可以用与此表观反应等价的耦合反应系统(包含所有的离子缔合反应)来解释Ca对硼酸弛豫参数的影响。     

Ultrasonic attenuation in the Gd-doped superconductor LaAl2

The ultrasonic attenuation (10–250MHz) in (LaGd)Al₂ with 0.23at% Gd has been measured between 293 K and 0.5 K. Below 10K the absorption is caused by superposition of phonon/electron absorption of Pippard type and a mechanical relaxation process which is attributed to a lattice defect of either vacancy, dislocation or impurity type. The relaxation takes place by interaction of the defect with both conduction electrons and lattice phonons with a mixed relaxation time. Superconductivity offers the unique chance to separate both relaxation mechanisms since during superconducting transition relaxation into the electronic system vanishes and leaves the phonon process alone to determine the defect dynamics. The temperature dependence of the individual relaxation times has been derived.     

Frequency dependence of ultrasonic absorption in mammalian testis

The earlier report that the frequency dependence of ultrasonic absorption of mammalian testis memicked a single relaxation process is explained as an effect of ultrasonic beam width upon the transient thermoelectric technique. More detailed measurements show that the frequency dependence of the ultrasonic absorption in testis is much the same as the attenuation in other soft tissues, viz., a proportional to f1.1. The earlier finding that testis exhibits an ultrasonic absorption coefficient significantly lower than reported for other tissues is confirmed.     

NMR and magnetic studies on 7 K anomaly in Tl3H(SO4)2

Measurements of the spin-lattice relaxation time, NMR absorption line and magnetization have been carried out on the Tl₃H(SO₄)₂ crystal below 50 K. The anomaly at around 7 K was: (1) the spin-lattice relaxation times of ¹H and ²⁰⁵Tl nuclei increase steeply with decreasing temperature below 7 K, (2) the NMR absorption lines below 7 K shift to the high-magnetic field side in comparison with that above 7 K, and (3) the ¹H NMR line width exhibits a drastic increase of the line width with decreasing temperature below 7 K. These results indicate that the magnetic dipole fluctuation of the proton changes at 7 K. On the other hand, there are no remarkable anomalies of magnetic susceptibility at around 7 K. From these results it is deduced that the anomaly at around 7 K is caused by the change in quantum mechanical process of the proton from proton tunneling to zero-point vibration of hydrogen in the hydrogen bond with the decrease of temperature.     

19F N.M.R. and 127I N.M.R. and N.Q.R. study of the molecular motions and deformations of iodine heptafluoride in its solid phases

In solid IF₇, ¹⁹F and ¹²⁷I N.M.R. and ¹²⁷I N.Q.R. absorption line shapes, frequencies and relaxation times have been studied from the melting temperature down to 56 K. Two new solid-solid transitions have been found at 180 K and 96 K in addition to the one already known at 153 K. The two high temperature phases are shown to be plastic. The fast molecular rotations and the slow molecular diffusion are studied from ¹⁹F and ¹²⁷I relaxation times. In the ordered phases, an analysis of the ¹⁹F second moments and longitudinal relaxation times shows the existence of a fast intramolecular exchange between axial and equatorial fluorine atoms, together with a much faster reorientation about the D ₅ axis. The characteristic times of these two motions are obtained and a mechanism for the exchange process is proposed. The chemical shift values of ¹²⁷I, the temperature dependence of the N.Q.R. frequencies and of the N.Q.R. relaxation times of ¹²⁷I, as well as the dipolar energy relaxation times have been measured and are discussed.     

Propagation of ultrasonic waves in neptunium monochalcogenides

The ultrasonic attenuation and acoustic coupling constants due to phonon–phonon interaction and thermoelastic relaxation mechanisms have been studied for longitudinal and shear waves in B₁ structured neptunium monochalcogenides NpX (X: S, Se, Te) along 〈1 0 0〉 direction in the temperature range 100–300 K. The second and third order elastic constants (SOEC and TOEC) of the chosen monochalcogenides are also computed for the evaluation of ultrasonic parameters. The ultrasonic attenuation due to phonon–phonon interaction process is predominant over thermoelastic relaxation process in these materials. The ultrasonic attenuation in NpTe has been found lesser than other materials NpS, NpSe and GdY (Y: P, As, Sb and Bi). The semiconducting or semimetallic nature of neptunium monochalcogenides can be well understood with the study of thermal relaxation time. Total ultrasonic attenuation in these materials is found to be quadratic function of temperature. The nature of NpTe is very similar to semimetallic GdP. The mechanical and ultrasonic study indicates that NpTe is more reliable, perfect, flawless material.     

Brillouin scattering in liquid sulfur dioxide: relaxational behaviour

The frequency dependence of hypersonic absorption and the dispersion of hypersonic speed in liquid sulfur dioxide (SO₂) were determined at (293.75±0.30) K and at (284.65±0.30) K by Brillouin spectroscopy. The results are used to experimentally establish the second relaxation step in the double vibrational relaxation of these quantities in the liquid phase, which was first conjectured by R. Bass and J. Lamb, Proc. R. Soc. Ser. A (1958) 243, 94. This second relaxation takes place at approximately 1.5 GHz for both temperatures within experimental error, whereas the first relaxation step, previously determined by ultrasonic spectroscopy, takes place at approximately 23 MHz. In the course of this investigation, some evidence was found that for the temperatures considered the shear viscosity relaxes in the hypersonic frequency range.     

Kernresonanz-und leitfähigkeitsmessungen zu diffusion und fehlordnung in LiBr

Electrical conductivity and nuclear magnetic relaxation rates were measured with pure and doped LiBr between 400 K and the melting point (824 K). Prevalent intrinsinc disorder was observed down to 470 K. The degree of thermal disorder is 5.10⁻⁷ at 470 K and 5.10⁻³ at the melting point. From the relaxation rates of ⁷Li, which are caused by Li-diffusion and nuclear dipole interaction, mean jump frequencies of the cations are derived. Conductivities calculated from these frequencies for a jump process via neighbouing cation vacancies are in perfect agreement with directly measured conductivities. From relaxation rates of ⁸¹Br with MgBr₂-doped crystals jump frequencies of vacancies were obtained which are again in good agreement with those derived from the conductivity data. The energies resulting from the measurements are (0.43 ± 0.03) eV for migration of cation vacancies and (1.46 ± 0.05) eV for thermal disorder. From motional narrowing of the ⁸¹Br absorption line the jump frequency of the anions is obtained, which is much smaller than for the cations. Since this motional narrowing is not influenced by any doping, it is concluded that anion transport mainly occurs via pairs of cation and anion vacancies.     

Mössbauer effect of57Fe in spin frustration system,CsCoCl3

The Mössbauer spectra of 3%⁵⁷Fe doped CsCoCl₃ revealed marked relaxation in all phases. The relaxation was interpreted in terms of propagating domain walls along the magnetic chains together with the transition between the lowest doublet and the low excited singlet levels. The hyperfine field of 24.5T was observed at 4.5K.