铋系氧化物高温超导相晶格软化研究

本文报道了在液氮温区以上铋系高 T_c 超导相变温穆斯堡尔谱的实验结果.穆斯堡尔无反冲因子随温度变化表明,在超导转变温度 T_c 以上,铋系高 T_c 相的 Cu-O 层中出现了明显的晶格软化现象,这种与晶格软化相联系的结构不稳定行为可认为是超导转变的前驱效应.在 Cu-O 层上发生的品格软化的特殊性质,对超导电性的影响不能忽略.     

氮离子注入纯铁中表面改性的穆斯堡尔谱研究

采用等离子体源离子注入方法,将氮离子注入纯铁粉中,对样品进行穆斯堡尔谱研究.对注氮前后样品的无反冲因子f、同质异能移位δ、电四极裂距ΔEQ进行了比较分析.解释了氮离子注入钢材表面其硬度和耐磨性提高的原因. 关键词：     

共价和极化对119Sn、129I 穆斯堡尔谱位移的影响

利用化学键的介电理论研究了＾１１９Ｓｎ、＾１２９Ｉ穆斯堡谱同质异能位移,发现由共价性ｆ＾μｃ和极化率α＾μＬ定义的化学环境因子ｈ与穆斯堡尔谱同质异能位移δ存在线性关系：δ＝δ０＋ｂｈ,ｈ＝（∑／μαＬ＾μｆ＾μｃ）＾１／２。     

人工合成铁叶啉Fe(OEP) Cl弛豫现象的穆斯堡尔研究

本文报道了人工合成铁叶啉-Fe(OEP)Cl,Fe(NO₂)(OEP)Cl和Fe(NO₂)₂(OEP)Cl,在77K、300K和室温下外加5KOe磁场时测得的穆斯堡尔谱。用电子自旋-自旋弛豫机制解释了谱线的变化,并讨论在叶淋环中位取代不同数目的(NO₂)基所引起同质异能移位的微小变化。     

计算机分析穆斯堡尔谱的方法

前言 穆斯堡尔效应是原子核对r射线的无反冲的共振吸收和发射现象,它是鲁道夫·勒·穆斯堡尔(LR.Mossbauer)在1957年发现的,故以他的名字命名.穆斯堡尔效应自发现以来,发展极其迅速,现已成为专门的学科─—穆斯堡尔谱学.穆斯堡尔效应的应用非常广泛,已经渗透到物理学、化学、矿     

铋钙钒石榴石型铁氧体穆斯堡尔效应的研究

穆斯堡尔效应是指固体中无反冲的核γ射线的共振吸收。利用这一效应可以研究固态物质的微观结构,例如磁超精细相互作用、电四极相互作用和同质异能移位等,以及微观结构与宏观性能的关系。通过这项研究,可以获得有关固体的晶体结构、电子构型、磁性和晶场等的认识。因此,在固体物理、磁学、材料科学以及化学、地球科学、生物学和工农业生产中,这一效应都越来越获得较为广泛的应用。     

高矫顽力型FeCrCo合金相变化的穆斯堡尔谱研究

通过穆斯堡尔谱、透射电镜、x射线和磁测量等手段研究了将普通FeCrCo合金中Cr,Co元素含 量提高、并加入Mo,Zr元素后合金矫顽力的变化，发现其值76kA/m比普通值40—52kA/m高50% 以上.对该合金不同热处理阶段的穆斯堡尔谱的测试表明，合金的微观结构与普通FeCrCo合 金有显著的不同.固溶处理后合金单相性好，不产生对磁性起破坏作用的γ相；磁场热处理 过程中，发生原子的重新排布，α₂相开始出现，两相结构基本确定；分级回火 后，调幅 分解进行得更彻底，合金内部完全形成调幅结构，与低矫顽力合金相比，铁磁性的α₁ 相更容易形成. 关键词： 穆斯堡尔谱 调幅分解 磁超精细场 同质异能移     

T1系超导体1223相的晶格振动行为研究

对不同铁掺杂量的Ｔ１系１２２３相样品，进行了室温Ｍｏｓｓｂａｕｅｒ谱测量及解谱分析．在７７Ｋ至室温范围作了变温Ｍｏｓｓｂａｕｅｒ谱测量．发现无反冲因子ｆ在Ｔｃ附近反常地下降，表明伴随着超导转变，在Ｔｃ附近晶格振动发生了反常的软化现象．     

界面活性剂对Fe3O4磁性与穆斯堡尔谱的影响

测量了不同颗粒尺寸Fe₃O₄覆盖界面活性剂前后磁性、红外谱以及穆斯堡尔谱。实验结果表明界面活性剂与Fe₃O₄微粒表面为化学吸附,覆盖界面活性剂后在相同磁场下磁化强度有所下降,穆斯堡尔谱变得弥散,随着颗粒尺寸变小,穆斯堡尔谱内场减小,谱线变得更为弥散,实验结果可以用表面各向异性的理论进行解释。 关键词：     

穆斯堡尔谱学讲习班简讯

1980年7月24日至8月16日在中国科学院物理研究所举办了穆斯堡尔谱学及非晶态磁学专题讲习班.由爱尔兰都柏林大学的J.MD.Coey博士主讲.与会单位有中国科学院的高能物理研究所、地质研究所、上海原子核研究所、冶金研究所、北京大学、清华大学和工厂等20多个单位,代表共有七十余人. J·M·D·Coey博士是一位博学多识,经验丰富的青年科学家.他讲学的主要内容:(1)穆斯堡尔效应的原理及其应用;(2)非晶态磁学,主要介绍他多年来的研究工作. 穆斯堡尔效应又称为无反冲γ射线共振吸收.Coey博士详细介绍了穆斯堡尔谱学的发展动态;阐明了测量穆斯堡…     

Effect of the features of the low-energy spectrum of vibrational states in disordered systems on the probability of the Mössbauer effect and the Debye-Waller temperature factor

We study the effect of the additional density of vibrational states inherent in disordered systems on the Mössbauer effect and the Debye-Waller temperature factor at temperatures of about 10 K. We show that the effect of the additional density of vibrational states shows up as an increase in the exponent in the temperature dependence of the mean-square displacement and should manifest itself in measurements of the temperature factor and the probability of a recoilless process.     

Low-temperature structure of Fe-Ni alloys

The Debye temperature (θ_M) of Fe-Ni alloys was obtained from measurements of the X-ray integrated intensity and the electrical resistivity at low temperatures from 4 to 300 K. A decrease of θ_M, implying a lattice softening effect, was found by lowering the temperature or increasing the iron concentration in the Invar region.     

Messung der rückstoßfreien Resonanz-Absorption am 6,2 keV-Niveau in181Ta

A strong recoilless resonance absorption was observed for the extraordinarily narrow 6.2 keV level (T _1/2=6.8 μs) of¹⁸¹Ta. Using sources of¹⁸¹W in W-metal and Ta-metal absorbers, a linewidth of about 9 times the natural width was obtained, with an enormous isomer shift of +(0.85±0.02) mm/sec, which is equivalent to a shift by 260 times the natural linewidth. Recoilless resonance spectra of cold worked and of oxygen doped absorbers showed a high sensitivity of the linewidth against lattice imperfections due to inhomogeneous quadrupole interactions and isomer shifts. Measurements of the residual resistivity ratio and of the lattice constant of the impurity doped absorbers yielded a linear correlation between linewidth and isomer shift.     

Size dependence of the Mössbauer effect in one-dimension

Employing a model of coupled harmonic oscillators we analyze the nature of recoilless emission in the Mössbauer effect for a finite sized 1D lattice. We demonstrate explicitly that under certain assumptions, recoilless probability first attains a maximum for a certain lattice size and then decreases with increasing lattice size. Further, we derive a scaling relation for this variation. Our treatment may have relevance to the recoilless probability in finite clusters such as nanocrystals and nanowires.     

Surface infra-red emission during alkali–metal incorporation at an oxide surface

Thermal emission of infra-red radiation from excited vibrational states is a sensitive probe of surface lattice dynamics, allowing the effects of adsorbed species to be studied in unprecedented detail. Here we examine the incorporation of adsorbed K into a NiO surface by following the formation of K₂O₂ and KNiO₂ through the evolution of the phonon spectrum. The resolution attained in the emission experiment yields new insight into processes of interdiffusion and growth. We identify O atoms as the mobile species at annealing temperatures up to 300 K, with K/Ni interdiffusion occurring after annealing at 600 K.     

Mössbauer spectroscopic study on SUS 304 foil at low temperature

Mössbauer parameters such as the line width and the absorption area of SUS 304 foils were observed to increase below 60K, but the change of the isomer shift below 60 K was not observed. The broadening of the line width were attributed to the effect of the magnetic transition at near 60K. On the increasing of the absorption area below 60K, two reasons were suggested. One is the increasing of the recoilless fraction of austenitic phase due to the magnetostriction effect. The other is that there is an unassigned phase below 60K and this phase come from interstitial trapping of⁵⁷Fe atoms which move in the cage.     

Vibrational properties of RbNd(WO4)2: high pressure Raman study, structural and phonon calculations

RbNd(WO(4))(2) was investigated by high pressure Raman spectroscopy in the 0.1-12.3 GPa pressure interval. The assignment of modes was made based on lattice dynamics calculations and the results of these calculations helped us to also discuss the high pressure behavior of phonon spectra in this material. Our results show that a double oxygen bridge plays a fundamental role in the vibrational properties of this system. A density functional theory (DFT) calculation of hydrostatic pressure effects on RbNd(WO(4))(2) was performed in order to understand the effect of internal bond changes on the vibrational properties of RbNd(WO(4))(2). No pressure induced structural phase transition was observed in the Raman study at room temperature, and the DFT calculation (T = 0 K) is consistent with this result. The anomalous softening of the bridge stretching mode at 770 cm(-1) was attributed to the decrease of W-O1-W bond angle with increasing pressure.     

Specific heat of the cubic high-Tc superconductor Ba0·6K0·4BiO3

We report magnetic susceptibility and specific heat measurements on polycrystalline samples of the 30 K superconductor Ba_0·6K_0·4BiO₃. Normal-state magnetization measurements indicate a Pauli-paramagnetic susceptibility of χ_pauli = 2.3 × 10⁻⁵ emu/mole, from which we infer a value for the density of states at the Fermi level of N(0) = 8.6 × 10 ²¹ev⁻¹cm.⁻³ Specific heat measurements performed between 1.6 K and 40 K indicate that considerable lattice softening occurs at low temperatures; the effective Debye temperature drops from 280 K at 35 K to 210 K at 4 K, implying that soft phonon modes are present in this compound. This result indicates that conventional phonon-mediated interactions may be responsible for the high transition temperature exhibited by Ba_0·6K_0·4BiO₃.     

Goldanskii effect in quadrupole Mössbauer spectra of the 89 keV gamma ray of 156Gd

Unusual relative line intensities in the recoilless absorption spectra of the 89 keV gamma ray of ¹⁵⁶Gd in Gd₂Ti₂O₇ have been observed at various temperatures. The results prove that the unusual intensities are mainly due to lattice vibrational anisotropy.     

High pressure of solid noble gases in metals

The fact that noble gas ions implanted in metals with concentrations of a few percent precipitate at room temperature as solid bubbles under high pressure with a structure epitaxial with the host matrix (fcc or hcp) has been investigated recently. A brief survey of the results measured by transmission electron microscopy, glancing angle X-ray diffraction, energy-loss spectroscopy and positron annihilation is given. The main part of this paper deals with a study on⁸³Kr⁺ implanted in Al using Mössbauer spectroscopy. The results are as follows: the precipitates grow from 1.5 nm after implantation to 3.7 nm after 700 K annealing. The recoilless fractions can be fitted very well to a Debye model. On annealing. the characteristic Mössbauer temperature gradually decreases from 89 K to 64 K, the value for solid Kr at 1 bar. At the same time a decrease in the isomer shift is observed. Even after annealing at 700 K our experiments do not show melting in the temperature range 0–230 K.