A.C. electrical conductivity of potassium perchlorate

A.C. electrical conductivity of pottasium perchlorate (KP) has been measured in the temperature range 25–325°C at frequencies ranging from 50–500 Hz using an automated technique. Three regions with activation energies. 1.08 ± 0.02, 0.66 ± 0.01 and 0.39 ± 0.04eV are observed in ln(σT) vs 1/T plots at frequencies < - 50 Hz. Dielectric loss measurements on KP samples doped with CrO₄^2? and SO₄^2? ions show the presence of impurity-vacancy complexes with reorientation energies of 0.99 ±0.02 and 1.07 ± 0.01 eV respectively. The results are interpreted in terms of a defect model which highlights the role of various conduction and relaxation mechanisms in the a.c. electrical properties of the material.     

Spin relaxation studies on conducting poly(tetrathiafulvalene)

Magnetic parameters and the relaxation behavior of paramagnetic centers in an iodine-doped poly(tetrathiafulvalene) semiconductor with a d.c. conductivity of 10^?5 S·cm^?1 have been studied using mainly the 2 mm waveband EPR technique in the temperature range of 110–270 K. The EPR line shape analysis confirms the existence of immobile radicals pinne on short polymer chains and mobile polarons with different relaxation parameters in slightly doped poly(tetrathiafulvalene). The temperature dependences of electron spin-lattice and spin-spin relaxation times of paramagnetic centers of both types have been determined independently using the saturation method at the operation frequency ν _e = 140 GHz. An anisotropic slow libration of immobile polarons with an activation energy of 0.02 eV have been registered for the first time using the saturation transfer EPR method. The temperature dependences of intrachain diffusion and interchain hopping rates in poly(tetrathiafulvalene) are determined from theT ₁ andT ₂ EPR data. The interchain spin dynamics is shown to correlate with libration of polarons trapped on polymer chains and is in good agreement with a hopping charge transport mechanism.     

Optical investigation of DyFeO3

Optical absorption spectra of DyFeO₃ have been investigated at 1.2≦T≦4.2 °K, andT=77 °K From the temperature dependent lineshift a Néel temperature ofT _N=(3.8±0.5) °K is deduced for the dysprosium sublattices. The groundstate splitting due to the iron-dysprosium interactions is about 1.5 cm^?1 and due to the dysprosiumdysprosium interactions (5.0±1.4) cm^?1. Zeeman studies give the magnetic moment of the dysprosium ions asμ=(9.2±1.0)μ _B.     

Electron spin-lattice relaxation anomaly and the local pseudo freeze-out of impurity dynamics in H-bonded ferroelectrics

The strong decrease in the electron spin-lattice relaxation rate at the ferroelectric transition temperature T_c and the simultaneous increase in the transverse spin-spin relaxation rate can be both understood in terms of the local “spontaneous freeze-out” model of impurity dynamics recently proposed to explain the spontaneous dynamic symmetry breaking observed far above T_c in the EPR spectra of H-bonded ferroelectrics doped with paramagnetic impurities.     

Fluorine mobility in an aluminum-doped CeF<Subscript>3</Subscript> crystal: NMR and conductivity studies

Electrical conductivity and NMR measurements were carried out for an aluminum-doped CeF₃ crystal to study the influence of substitutional impurities on the superionic fluorine mobility. Activation enthalpy was found to remain constant from low temperatures to about 325 K and to increase as compared to that of a pure CeF₃ crystal. Above about 325 K, a trend towards gradual conductivity saturation was observed. This change was ascribed to a superionic phase transition not accompanied by structural transformations. NMR also revealed some alterations in the local fluorine dynamics as compared to that reported for a pure CeF₃ crystal. According to NMR measurements, the superionic phase transition near 325 K results in acceleration of the exchange between rigid or slow fluorine in the F₁, F₂, and F₃ sublattices, while highly mobile F₁ fluorine ions move independently at least until 400 K.     

Critical nuclear relaxation in cobalt metal

Nuclear magnetic resonance of cobalt metal was investigated in the paramagnetic and ferromagnetic states and in the critical region below T_c. The Knight shift and spin lattice relaxation times were measured in the paramagnetic phase in the solid and liquid states from 1578 K to 1825 K. The resonant frequency, spin-lattice and spin-spin relaxation times were measured in the ferromagnetic phase from room temperature to 1385 K. The main part of (T₁T)^-1 results from fluctuating orbital moments in both phases except near T_c where this process forms the background for critical spin relaxation. The critical exponents for T^-1₁ and for the magnetization in the ferromagnetic state were found to be n' = 0.96 ± 0.07 and β = 0.308 ± 0.012, respectively.     

Oxidised polyethylene as a paraelectric

A new experimental study of a known low temperature dielectric relaxation in oxidised polyethylene confirms that it is a manifestation of paraelectricity with certain similarities to the doped alkali halide systems. The tunnel splitting parameter (half the minimum energy splitting) is found to be 3.9 μeV ± 10%, while the strain coefficient of the double-well asymmetry is ≈ 5 meV. The multiphonon regime takes over from the one-phonon range at characteristic temperature T_o = 7.2 ± 0.5 K. A rather well oxidised sample shows a relaxation rate which varies as T^0.4 when T < 1 K, while the spread becomes markedly broader than a Debye curve. Oxidation with O₂¹⁸ leads to a 4.2 K peak at a frequency 13–15% lower than oxidation with O₂¹⁶. When the oxidised polyethylene is vacuum annealed the relaxation intensity diminishes. The half life at 126 C is about 2 hr and the activation energy of the annealing process is 40 ± 5 kcal/mole. A contaminated specimen showed accelerated oxidation kinetics and also accelerated anneal effect. These results lead to a suggested attribution of the relaxation to the rotation of the dihedral angle of isolated hydroperoxide groups. It is suggested that other hydrocarbon type materials may exhibit paraelectricity.     

Photoluminescence measurements of the 1.55 eV band of Ge doped AℓxGa1−xAs

The photoluminescence of the 1.55 eV band of Ge doped A?_xGa_1?xAs, with x=0.30–0.33, grown by liquid phase epitaxy is presented. The broad shape was found to be due to a lattice relaxation upon optical transitions. Resonant modes with ?ω_q = 35±2 meV and ?ω_q = 45±2 meV are found for the optical band, yielding a zero phonon transition energy = 1.73±0.02 eV and a Franck-Condon shift = 0.17–0.20 eV for the optical center. The activation energy of thermal quenching yields an associated donnor binding energy of 0.17±0.04 eV. Possible mechanisms for the radiative transitions are discussed.     

Impurity 55Mn NMR in Cu-Mn dilute alloys

We detected impurity ⁵⁵Mn NMR in Cu-45 ppm and -110 ppm Mn dilute alloys at temperatures of 150–330 K. The hyperfine field we obtained was 65±5 kOe/μ_B. From a temperature variation of linewidths we could estimate J_sd as 1.2±0.1 eV, using the reported theories of relaxation times T₁ and T₂.     

Temperature measurement of 6He?+? ions confined in a transparent Paul trap

The LPCTrap setup is a transparent Paul trap dedicated to the measurement of the ???C?? correlation coefficient a _?|? in the ?? decay of trapped radioactive nuclides. In a first experiment, the system has been used to record ??10⁵ coincidences between the ?? particles and recoiling ions emitted from the decay of ⁶He^?+? ions. The analysis of the collected data has already shown that the size of the ⁶He^?+? ion cloud confined in the Paul trap is a critical parameter, potentially limiting the accuracy on the a _?|? measurement. We report here the precise determination of the trapped ion cloud temperature and size. This was performed by extracting the trapped ions toward a position sensitive micro channel plate detector at different phases of the RF driving field. We find a temperature T _exp ?= 0.107(7) eV, consistent with the temperature values inferred using two other observables but 20% higher than the temperature T _sim ?= 0.09 eV predicted by realistic simulations of the ions interacting with the H₂ buffer gas.     

Specific features of anion transfer in HoF<Subscript>3</Subscript> crystals at high temperatures

The anionic conductivity of HoF₃ single crystals with a β-YF₃ structure (orthorhombic crystal system, space group Pnma) is investigated over a wide range of temperatures (323–1073 K). The unit cell parameters of HoF₃ crystals are as follows: a=0.6384±0.0009 nm, b=0.6844±0.0009 nm, and c=0.4356±0.0005 nm. It is revealed that the conductivity anisotropy of the HoF₃ crystals is insignificant over the entire temperature range covered. The crossover from one mechanism of ion transfer to another mechanism is observed near the critical temperature T_c≈620 K. The activation enthalpy of electrical conduction is found to be ΔH₁=0.744 eV at T<T_c and ΔH₂=0.43 eV at T>T_c. The fluorine vacancies are the most probable charge carriers in HoF₃ crystals. The fluorine ionic conductivities at temperatures of 323, 500, and 1073 K are equal to 5×10^?10, 5×10^?6, and 2×10^?3 S cm^?1, respectively.     

Origin of dielectric relaxations in KHSeO4 above room temperature

The dispersion curves of the dielectric response for KHSeO₄ were obtained in the radio frequency range at several isotherms below the fast proton conducting phase (T?<?415 K). The results reveal a distinct dielectric relaxation at low frequency, which is about 682 Hz at 320 K, and then, it shifts to higher frequencies (～10 kHz) as the temperature increases. The f _max vs. reciprocal T shows an activated relaxation process with an activation energy of 0.5 eV, which is in close agreement with that associated with transport of charge carriers. We suggest that the observed dielectric relaxation could be attributed to polarization induced by the proton jump and selenate tetrahedral reorientations. The displacement of mobile H⁺ proton accompanied by SeO ₄ ^??2 tetrahedra reorientations creates structural distortion in both sublattices which induce localized dipoles like HSeO ₄ ^? .     

Effect of cascading of higher-lying states on a delayed 1s-2p transition after beam-foil excitation of 56 MeV hydrogen-like oxygen and fluorine

The delayed fluorescence of the soft X-ray (1s-2p) transition was observed for H-like ions (O⁷⁺ and F⁸⁺) between 1.3 ns and 20 ns decay time after beam-foil excitation. The delayed X-ray fluorescence was found to decay with at ^Δ power law time dependence. The non-exponential decay is attributed to cascading through higher lying states. We found thatΔ ₀=1.40±0.08 andΔ _F =1.44±0.02 for H-like oxygen and fluorine, respectively. Present results are in fair agreement with the previously reported exponent,Δ ₀=1.5, measured over 3 ns after excitation.     

Transient optical absorption induced by an electron pulse in KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript> crystals

The efficiency of formation and time evolution of radiation-induced structural defects and pulsed luminescence in KPb₂Cl₅ crystals under the action of a single electron pulse (E = 250 keV, τ = 20 ns) have been investigated. The spectra (1.1–3.8 eV) and relaxation kinetics (time interval 5 × 10^?8?5 s) of transient optical absorption and the pulsed cathodoluminescence spectra and decay kinetics (1.4–3.1 eV) have been measured in the temperature range 80–300 K. It is revealed that the induced optical density and its time evolution depend strongly on temperature, and the absorption relaxation time contains several components and reaches several seconds at T = 300 K. The decay kinetics of transient absorption and pulsed cathodoluminescence kinetics have different orders and are controlled by different relaxation processes.     

Injection and thermodepolarization currents in GaSe <Co> single crystals

The current-voltage characteristics (CVC) at different temperatures, the temperature dependence of electric conductivity [σ(T)] and the currents of thermostimulated depolarization (TSD) have been studied in GaSe <0.05 at.% Co> on a combined basis.The location depth (E_t=0.57eV) and the concentration of traps (N_t=2.7x10¹²cm^?3) have been determined from the temperature dependence of the trapping factor. In the course of TSD investigations, levels with location depths of 0.28±0.02 and 0.57±0.03 eV have been revealed. It is noted that traps with the energy of 0.57±0.03 eV are found both with TSD measurements and on the basis of the temperature dependence of the electric conductivity and the trapping factor.It has been established that the hole centres above the valence band are responsible for the CVC, σ(T) and TSD. The location depths, concentrations and trapping cross-sections of these centres have been determined.     

Electron spinT 2 of a nitroxyl radical at 250 MHz measured by rapid-scan EPR

Rapid-scan electron paramagnetic resonance (EPR) was used to measure the room temperature spin-spin relaxation timeT ₂ for the per-deuterated nitroxyl radical, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl-d₁₆ in water at 250 MHz. Signals were recorded on a locally constructed system using either sinusoidal or triangular magnetic field scans. Values ofT ₂ were obtained by simulation of the rapid-scan response and were systematically shorter for the high-field line (m ₁=?1) than for them ₁=0 or +1 lines. Form ₁=+1, the value ofT ₂ increased from 0.41±0.03 μs at 0.5 mM to 0.53±0.03 μs at 0.1 or 0.2 mM. Form ₁=?1,T ₂ increased from 0.35±0.03 μs at 0.5 mM to 0.42±0.03 μs at 0.1 or 0.2 mM. These values put lower bounds on the values ofT ₁ for this nitroxyl at 250 MHz.     

Migration and stabilization of hydrogen atoms in KCl

Stabilities of hydrogen atoms at the interstitial (H⁰_i), cation and anion sites (H⁰_sc and H⁰_sa) in KCl have been studied with ESR and thermoluminescence. The close pair between H⁰_i and S^? formed by UV-irradiation of KCl:SH^? recombines first with the activation energy of 0.17±0.02 eV following the emission of light and then H⁰_i becomes mobile with the energy of 0.20±0.02 eV. The energies determined from the decay of ESR signal intensity of H⁰_sc and H⁰_sa are 0.24±0.02 eV and 0.43±0.03 eV, respectively.     

非晶锂离子导体B2O3-0.7Li2O-0.7LiCl-xAl2O3晶化初期的核磁共振研究

通过真空密封热处理、避免了样品晶化后吸水引起的误差,采用脉冲法在293K和77K测量了晶化过程初期三种非晶锂离子导体B₂O₃-0.7Li₂O-0.7LiCl-xAl₂O₃(x=0.15,0.10和0.05)的⁷Li核磁共振谱。发现在低温(77K)只有固相锂离子对应的自旋-自旋弛豫时间T₂=87μs,严格按高斯函数衰减。在室温下固相锂离子对应的T_2s=127μs,仍是高斯型;但液相锂离子对应的T₂却按洛仑兹函数衰减。这反映出锂离子导体的固-液二相性。三种非晶B₂O₃-0.7Li₂O-0.7LiCl-xAl₂O₃(x=0.15,0.10和0.05)分别在热处理温度401,388和381℃附近,其液相锂离子对应的T_2l都剧增,其吸收谱线宽都变窄。由此再次验证了非晶母体与微晶之间的两相界面效应的物理图象。 关键词：     

Electronic structure and indirect spin-spin interactions in bournonite (CuPbSbS3) according to antimony nuclear quadrupole resonance

A complex sulfide CuPbSbS₃ (bournonite) has been studied by the nuclear quadrupole resonance on ^121,123Sb. The temperature dependences of the spectroscopic and relaxation parameters in the temperature range of 10–295 K have been obtained. The crystallochemical features of the environment of the two non-equivalent Sb positions in the unit cell have been revealed from the nuclear quadrupole resonance spectra. The existence of the lattice vibrations with the frequency ω = 110 cm^?1 has been demonstrated on the basis of the temperature dependence of the nuclear quadrupole resonance frequencies. Slow beats have been observed on the decay curve of the spin echo signal. Experimental data have been analyzed in order to reveal the existence of the indirect spin-spin interactions involving Sb atoms. The indirect spin-spin coupling constant has been estimated as J = 2.5 ± 0.5 kHz.     

Mössbauer effect studies of spin-spin relaxation in single crystals of Fe(NO3)3·9H2O at 4.2 K

The spin-spin relaxation of Fe³⁺ ions in Fe(NO₃)₃·9H₂O single crystals has been studied at 4.2 K in the presence of external fields up to 80 kG. It is found that the spin-spin relaxation frequency varies substantially when the field direction is changed. Furthermore, the relaxation frequency increases with increasing applied field. Both effects are in agreement with the spin-spin relaxation theory of Bloembergen et al.