Paramagnetic hyperfine structure of193Ir in K2IrCl6 diluted into K2PtCl6

The paramagnetic hyperfine splitting of Ir⁴⁺ (5d⁵) in K₂IrCl₆ diluted into diamagnetic K₂PtCl₆ has been observed at 4.2 K and Ir∶Pt ratios of 1∶10 and 1∶25. In the latter case a narrow paramagnetic pattern with a hyperfine coupling constant ofA=−13.1(2) mm/s was observed, but both samples also exhibit a single Ir⁴⁺ line typical for fast relaxation, either because of macroscopic inhomogeneities in the Ir distribution or because part of the Ir spins are still coupled to nearest Ir neighbours.     

TDPAC study in ZnTiF6·6H2O between room temperature and 1273 K

Using the time differential perturbed angular correlation technique, the hyperfine interactions as titanium sites in ZnTiF6·6H₂O and its decomposition products were determined between room temperature (300 K) and 1273 K. The different steps in the decomposition pattern were identified and a simple model is given for it.     

Ionic conductivity of mixed K(NbW)O6 and KH2O(NbW)O6

The mixed oxides K(NbW)O₆ and KH₂O(NbW)O₆ were prepared by solid state reactions and characterized by X-Ray diffraction powder method, thermogravimetric analysis and differential scanning calorimetry. Electrical conductivity measurements were recorded between 190 and 508 K by the complex impedance method.     

Ultrasonic investigation of phase transitions in K2SnCl6

The velocities and the attenuation of ultrasonic waves have been investigated as a function of temperature (255KT350K) for the cubic phase of K₂SnCl₆ which undergoes a structural transition atT _c1263K. An anomalous decrease of the shear stiffness constantc=1/2(c ₁₁ –c ₁₂) of about 30% between room temperature andT _c1 is found in this cubic high temperature phase whenT _c1 is approached from above. Whereas the softening ofc extends over a substantial temperature range (about 50 K), the other shear constantc ₄₄ shows only a weak decrease, which is an order of magnitude smaller and restricted toT–T _c110 K. NearT _c1, a strong increase occurs in the attenuation of the shear acoustic wave propagated along the [111] direction, while such an anomalous attenuation is not observed for the transverse acoustic wave propagated along [100]. Furthermore, atT _c1 a hysteresis is detected for the longitudinal sound wave velocityv _L[100], which is restricted to the temperature region 262KT263.5 K. In addition, the room-temperature elastic constants of (NH₄)₂SiF₆ and the hydrostatic pressure derivatives of the elastic constants of K₂SnCl₆ and (NH₄)₂SiF₆ at room-temperature are presented and discussed in terms of mode softening behaviour.     

Inelastic neutron scattering by the quasi two-dimensional librational modes in K2SnCl6

The origin of the diffuse streaks observed in the high temperature phase of K₂SnCl₆ is explained in terms of a dynamical model in which [SnCl₆] octahedra are coupled by torsional springs. The magnitude and the temperature dependence of the torsional spring constants is derived from inelastic neutron scattering data. The librational modes are soft and overdamped at room temperature, and a central component is observed up to 170 K above the lattice instability which occurs atT _c1 =261.5 K.     

Temperature dependence of the diffuse streak system in K2SnCl6

We have investigated the system of diffuse streaks in K₂SnCl₆ single crystals in the temperature interval from 4 to 640 K by the photographic registration of the scattered neutron intensity. The streak intensity decreases from T_{c¹ = 261 K} with increasing as well as with In the region of the phase transition at T_{c¹ = 261 K} and T_{c² = 255 K} the intensity decreases with falling temperature to one third. The high temperature behaviour is explained by a soft A_2g librational mode. Below T_{c² = 255 K} the intensity is proportional to ΔT. The streaks are detectable down to 230 K.     

Hyperfine interactions in Li2ZrF6 and Li2HfF6

The quadrupole hyperfine interaction in Li₂ZrF₆ and Li₂HfF₆ has been studied as a function of temperature. Both lattices are characterized by very similar low and symmetric electric field gradients at probe sites and no phase transitions were observed up to 770 K. On heating, between 700 and 830 K, the Li₂ZrF₆ undergoes chemical reactions which give rise to ZrO₂ and then to Li₃ZrF₇ (high temperature α-phase) and Li₂ZrO₃. On cooling, below 750 K, the α→β transition in Li₃ ZrF₇ already reported is found to take place. An analogous behaviour is determined for Li₂HfF₆. Accordingly, the same decomposition steps and exstence of high and low temperature phases for Li₃HfF₇ can be inferred.     

Mössbauer spectra on [Fe(H2O)6]K2(SO4)2 exhibit slow electronic relaxation

Mössbauer spectra on single crystals of [Fe(H₂O)₆]K₂(SO₄)₂ in fields from 1.5 T to 5 T at temperatures from 4.2 K to 20 K show considerable line broadenings up to 0.95 mm/s. This broadening strongly depends on the specific line in the spectrum, the temperature, and the strength and direction of the external field. It is shown that these phenomena are due to electronic relaxation rates that are some-what slower (≈10^?8 s) than the fast relaxation limit.     

Ag/K_4Nb_6O_(17)异质结催化剂的制备、光谱分析及光催化性能研究

采用低温水热法成功制备了层状的K4Nb6O17半导体光催化材料。考虑到水热合成的K4Nb6O17表面多羟基(Nb—OH)和端氧(Nb O,Nb—O-)的特点,采用Ag(en)2+配合物前驱体法制备了高度均匀分散的Ag/K4Nb6O17异质结光催化剂,光催化性能评价结果表明,半导体K4Nb6O17表面负载极少量的Ag,其光催化降解甲基橙活性便得到大幅度提高,Ag的最佳负载量为0.5 at%。综合XRD,FTIR,UV-VisDRS,XRF和TEM表征结果,对Ag/K4Nb6O17异质结光催化剂的作用机制进行了较详细地阐述并获得如下结论:(1)K4Nb6O17提供了降解有机染料分子的电子和空穴;(2)K4Nb6O17纳米晶上Ag粒子作为光生电子接受器,促进了金属-半导体界面上电荷的转移,有效地分离了光生电子-空穴对,提高了光催化活性。     

Summary of ISNP2K

This is a brief summary of the ISNP2K (International Symposium on Nuclear Physics, 2000). Many interesting works were presented on new developments and perspectives of nuclear physics in the plenary and poster sessions. Subjects discussed are 1) high temperature and high density nuclei, new QGP phases and relativistic HI collisions, 2) new degrees of freedoms studied by medium energy reactions, 3) exotic nuclei with large isospin, large A, high J and high E _x , 4) new dynamical properties of many body nucleon systems, 5) neutrino nuclear physics and neutrons for astroparticle physics, and 6) new accelerators and new applications. ISNP2K with extensive discussions on nuclear physics frontiers at the turning point from 2000 to 2001 provides a good bridge to the new century.     

Development of NaCl:K(6T) phosphor for thermoluminescence dosimetry

The present paper discusses the development of the NaCl:K (10 ^–1 molar fraction of potassium) phosphor as dosimeter material for beta-radiation thermoluminescent dosimetry (TLD). The TLD grade NaCl:K(6T) material was prepared by annealing the NaCl:K powder obtained from aqueous solution by the method of recrystalization and annealed at 600°C for two hours in open air. It is observed that thermal glow curves of NaCl:K(6T) specimen exhibit well defined glow peak around 170°C alongwith a weaker peak at lower temperature. The high-temperature peak is found to grow supralinearily with increase in beta dose in the range 10–2×10³ rad. Since the nature of glow curves under the influence of different doses remains more or less identical, it is believed that the phosphor does not undergo radiation damage and give high intrinsic TL around peak III. Examination of the system for fundamental dosimetry requirement shows that the NaCl:K(6T) material can be used as a suitable TLD material in beta radiation.     

Results from solar, atmospheric and K2K experiments and future possibilities with T2K

Recent results from solar, reactor, atmospheric and long baseline (K2K) experiments are discussed. With the improved data statistics and analyses, our knowledge on the neutrino masses and mixing angles are steadily improving. T2K is the next generation neutrino oscillation experiment between J-PARC in Tokai and Super-Kamiokande. This experiment will start in 2009. This experiment is expected to improve the current knowledge on the neutrino masses and mixings substantially.     

High-resolution TDPAC measurement in K2ZrF6

A time resolution of 2=0.75 ns, achieved with a conventional TDPAC setup with FCs detectors, allowed a determination of the very high electric field gradient at Hf impurity sites in K₂ZrF₆.Simple theoretical calculations seem to indicate that nearest neighbours are responsible for the interaction observed.     

Raman and IR spectra of K4Nb6O17and K4Nb6O17·3H2O single crystals

Polarised Raman and IR spectra of K₄Nb₆O₁₇ and K₄Nb₆O₁₇· 3H₂O single crystals were measured. The obtained spectra are discussed using the factor group approach for the orthorhombic P2₁nb space group and assignment of bands to the respective motions of atoms is proposed. In particular, we have shown that the bands above 770 cm⁻¹ can be attributed to the stretching modes of short niobium–oxygen bonds, which are present in this material due to the pronounced layered structure, whereas the potassium atoms contribute to the bands observed below 180 cm⁻¹. Our studies have revealed that intercalation of water molecules leads to shifts, broadening and changes in intensity of some bands. These changes have been attributed to slight changes in the bond lengths and angles, interactions of the water molecules with K atoms and structural disorder introduced by the intercalated water molecules. However, the main structural framework was preserved. Copyright © 2010 John Wiley & Sons, Ltd.     

TDPAC study of the thermal evolution of the quadrupole parameters in NiTiF6·6H2O between 30 and 400 K

The thermal evolution of the quadrupole parameters determined using the time differential perturbed angular correlation technique at titanium sites, in NiTiF₆·6H₂O is presented. The study of the thermal behavior of the hyperfine quadrupole interaction allows one to observe the occurrence of a structural phase transition around 140 K. The thermal evolution of the hyperfine quadrupole frequency of the high temperature phase was interpreted in terms of the flip motion of the water molecules through an ad hoc model. Parameters associated with the model are in good agreement with independent data obtained by Raman scattering. The agreement gives support to the model to be a valuable tool to study the dynamics of molecular groups in crystalline hydrates.     

Observation of multiferroic properties in pyroxene NaFeGe2O6

We report the observation of multiferroicity in a clinopyroxene NaFeGe(2)O(6) polycrystal from the investigation of its electrical and magnetic properties. Following the previously known first magnetic transition at T(N1) = 13 K, a second magnetic transition appears at T(N2) = 11.8 K in the temperature dependence of the magnetization. A ferroelectric polarization starts to develop clearly at T(N2) rather than T(N1) and its magnitude increases up to ~13 μC m(-2) at 5 K, supporting the idea that the ferroelectric state in NaFeGe(2)O(6) stems from a helical spin order stabilized below T(N2). When a magnetic field of 90 kOe is applied, the electric polarization decreases to 9 μC m(-2) and T(N2) slightly increases by 0.5 K. At intermediate magnetic fields, around 28 and 78 kOe, anomalies in the magnetoelectric current, magnetoelectric susceptibility, and field derivative of magnetization curves are found, indicating field-induced spin-state transitions. Based on these electrical and magnetic properties, we provide a detailed low temperature phase diagram up to 90 kOe, and discuss the nature of each phase of NaFeGe(2)O(6).     

Temperature-dependent hyperfine parameters in CaFeSi2O6

Two samples of natural hedenbergite CaFeSi₂O₆ were studied in the temperature range from 4.2 K to 295 K, and at 78 K and 295 K in magnetic fields from 4.5 T to 7.5 T. The sign of V_ZZ is positive at 4.2 and 78 K and negative at 295 K. The asymmetry parameter depends strongly on the temperature. These results are explained by a simple model assuming a nondegenerated orbital doublet as ground state of Fe²⁺.     

Studies of the thermodynamic properties of the ordered perovskites Pb2CdWO6 and Pb2YbTaO6 within a broad temperature range

This paper reports on measurements of the specific heat of Pb₂CdWO₆ made at temperatures ranging from 80 to 750 K and of Pb₂YbTaO₆ within the 350-to 700-K temperature range. First-order phase transitions from the cubic phase at 677.3 and 581 K, respectively, were observed, and their thermodynamic characteristics were determined. The entropy change on the phase transitions is close to Rln4 for both compounds. The results obtained are discussed in terms of the model of position disordering of the lead ions. It was established that below 350 K, Pb₂CdWO₆ can exist in two states, stable and metastable, depending on the sample thermal prehistory.     

On the K^＋—^6Li Elastic Scattering

Total and differential cross sections for K^ -^6Li elastic scattering are calculated using the folding optical potential model,in which the influence of three factors is considered including the recoil of target nucleus,the loosely bounded nuclear density and the unusual spin of ^6Li ground state.The theoretical results are found in pretty good accordance with the existing experimental data at PK=715 MeV/c.     

Feshbach-resonant interactions in 40K and 6Li degenerate Fermi gases

We theoretically examine a system of Fermi degenerate atoms coupled to bosonic molecules by a Feshbach resonance, focusing on the superfluid transition to a molecular Bose-Einstein condensate dressed by Cooper pairs of atoms. This problem raises interest because it is unclear at present whether bimodal density distributions observed recently in 40K and 6Li are due to a condensate of bosonic molecules or fermionic atom pairs. As opposed to 40K, we find that any measurable fraction of above-threshold bosonic molecules is necessarily absent for the 6Li system in question, which strongly implicates Cooper pairs as the culprit behind its bimodal distributions.