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41.
In this work, the hyperfine quadrupole interaction at Ta-doped PbTi1−xHfxO3 polycrystalline samples is studied for the first time. Powders with x=0.25, 0.50 and 0.75 were prepared and characterized by X-ray diffraction analysis. Perturbed Angular Correlation (PAC) analyses were done as a function of temperature, using low concentration 181Ta nuclei as probes. In the ferroelectric and paraelectric phases of these compounds two sites were occupied by the probes. For each site the quadrupole frequency, asymmetry and relative distribution width parameters were obtained as a function of temperature above and below the Curie temperature (TC). One of these sites was assigned to the regular Ti–Hf site, while the other one was assigned to some kind of defect. The behavior of the hyperfine parameters as a function of temperature was analyzed in terms of a recent published phase diagram and the presence of disorder below and above TC. For the three compositions measured, the obtained hyperfine parameters present discontinuities which correspond to the ferroelectric–paraelectric phase transition. In both phases it was found broad frequency distributed interactions. The disorder in the electronic distribution would be responsible for the broad line width of the hyperfine interaction.  相似文献   
42.
The structure of biological molecules plays an important role in many biological processes. The variation of ambient parameters such as pH, temperature or pressure can influence important properties of protein molecules like conformation or stability. By means of the perturbed angular correlation (PAC) technique and atomic force microscopy (AFM) a conformation change of bovine serum albumin (BSA) molecules has been studied as a function of the pH value of the BSA solution. The observed decrease of the rotational correlation time and the increase of molecule diameter as a function of pH were attributed to conformational changes of bovine serum albumin induced by different pH values of the BSA solution.  相似文献   
43.
Although Cd and Ca ions have the same valence and cation size, their incorporation into vacancy-doped La manganites induce different properties. While the incorporation of Ca leads to high Tc up to 250 K and induces a metallic-like behaviour, the incorporation of Cd severely reduces Tc and promotes insulator-like behaviour. In this work, the Cd hyperfine fields have been measured with the Perturbed Angular Correlations (PAC) technique after implantation and annealing of 111mCd in La–Cd–MnO3 samples. The PAC results are compared with measurements of the resistivity and magnetization performed on the same samples. The mixed La and Mn site Cd occupancy is suggested as a possibility to explain the properties of the La–Cd–MnO3 system.  相似文献   
44.
增效反应中聚合氯化铝红外结构特征的变化   总被引:9,自引:0,他引:9  
对聚合氯化铝 (PAC)进行增效改性是制备高性能无机高分子絮凝剂的重要手段之一。用多核络合剂络合、聚合硅酸交联和聚丙烯酰胺复合三种增效方法改性PAC ,分别获得了结构有别于PAC的新型絮凝剂CO PAC ,CR PAC和PAM PAC。其傅里叶红外光谱 (FTIR)表明 ,在三种无机高分子结构中均存在Al—OH以外的新化学键 ,且原有基团的特征吸收峰位置因受结构畸变而发生一定的低频红移 ,证实了PAC增效反应并不是单纯的物理混合加成作用 ,而是形成了具有特殊结构的无机高分子的化学反应。这类无机高分子絮凝剂所具有的优良絮凝特性是由增效剂和PAC间以化学作用为主的物理化学因素共同作用的结果。  相似文献   
45.
Nuclear quadrupole interactions of 111Cd probes in In2La and CeIn2 were measured using perturbed angular correlation of gamma rays (PAC). Near room temperature, a single non-axially symmetric quadrupole interaction was observed in each compound, with ω 0 = eQV zz /ℏ = 78.8(2) Mrad/s and η = 0.312(1) for In2La at 11°C and ω 0 = 80(1) Mrad/s and η = 0.29(2) for CeIn2 at 34°C. The observed non-axial symmetry is consistent with the reported CeCu2 structure of the phases. The non-axially symmetric interactions were replaced completely by axially symmetric interactions (η = 0) at 524°C, with ω 0 = 101.0(1) Mrad/s in In2La and ω 0 = 96.9(4) Mrad/s in CeIn2. The change in symmetry is attributed to a polymorphic phase transformation. Based on symmetry information from the quadrupole interaction and on chemical arguments, it is proposed that high-temperature phases of In2La and CeIn2 both have the AlB2 (C32) structure.  相似文献   
46.
The amorphous ferromagnetic alloy Fe79/B16/Si5 was investigated by PAC. For that the probe atoms 111In(111Cd) and 111mCd were implanted at the ISOLDE on-line separator. The distributions of magnetic hyperfine fields were determined. Below the crystallization temperature α-Fe clusters could be observed. For comparison Mössbauer transmission experiments were performed.  相似文献   
47.
Rais  A.  Yousif  A. A.  Gismelseed  A.  Elzain  M. E.  Al Rawas  A.  Al-Omari  I. A. 《Hyperfine Interactions》2004,158(1-4):229-233
PAC measurements on 111In(111Cd) implanted and thermally treated α-Fe have shown an indication for a cubic defect with the 111Cd probe in the centre of it. The measured room temperature (R. T.) magnetic hyperfine fields are B hf1 = −38.4(8) T for substitution and B hf2 = +11.5(3) T for the cubic defect. Additionally, probes with pure quadrupole frequency distributions were observed, which are incorporated in surface contaminations.  相似文献   
48.
The usefulness of local hyperfine techniques in the investigation of the physical properties of Kondo lattices is illustrated through three examples. First, we show how Mössbauer spectroscopy on 170Yb down to very low temperature (0.025 K) provides evidence for the existence of an incommensurate modulated magnetic structure close to T=0 in YbPtAl; a modulated structure at T=0 is in principle forbidden for Kramers ions, but it is made possible in YbPtAl due to the presence of the Kondo coupling. Second, we present a μSR study of the Kondo insulator YbB12, and we evidence the persistence of fluctuations of very small correlated Yb moments close to T=0. Third, we report on a study by Perturbed Angular Correlation spectroscopy on the isotope 172Yb of the Kondo lattice Yb2Co3Ga9, which is characterised by a high Kondo temperature (T 0?260 K). Our aim was to compare, on a large temperature range, the thermal variations of the 4f quadrupole moment and of the magnetic susceptibility, to check whether the scaling property predicted by theory could be observed.  相似文献   
49.
The perturbed angular correlation (PAC) technique was applied to study the electric field gradients at 111In sites in CdIn2O4. The measurements were carried out at temperatures in the range 150–1073 K. The aims of the study were both to characterize the quadrupole interactions of the tracers and to determine the distribution of indium ions among the available sites in the spinel structure. Room temperature measurements corresponding to samples cooled at different rates are also reported. aAlso at Comisión de Investigasiones Científicas de la Provincia de Buenos Aires, Argentina.  相似文献   
50.
The magnetic response of europium in γ-cerium and in platinum was studied by applying the perturbed angular correlation spectroscopy. The probe nuclei were 147Eu(11/2) and 149Eu(11/2). The response in γ-Ce was determined by the electronic S = J = 7/2 ground state of divalent Eu. In Pt, on the other hand, Eu is trivalent (J = 0 ground state). Here the magnetic contributions originate from Van Vleck terms of the whole multiplet system.  相似文献   
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