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1.
The temperature dependence of the impurity optical absorption of nominally pure Bi12SiO20 (BSO) crystals and BSO crystals doped with Ga, Cr, Mn, and Ag ions is investigated. A method is proposed for determining the thermal activation energy, and certain properties of deep levels are found. Fiz. Tverd. Tela (St. Petersburg) 40, 452–457 (March 1998)  相似文献   

2.
The spectral distribution of the uv-induced photoconductivity intensity and relaxation in Bi12SiO20 and Bi12GeO20 crystals both undoped and doped with Al, Ga, Cr, Cu, Mn, and V is investigated in the optical range 0.5–3.5 eV in the temperature ranges 85–95 K and 285–295 K. It is shown that in the short-wavelength region 2.2–3.5 eV it is controlled by multicenter recombination in which both “fast” and “slow” recombination participate. Fiz. Tverd. Tela (St. Petersburg) 40, 1027–1029 (June 1998)  相似文献   

3.
The AC conductivity of the LiCaPO4 compound has been measured in the temperature range 634–755 K and the frequency range 300 Hz–5 MHz. The impedance data were fitted to an equivalent circuit consisting of series combination of grains, grains boundary, and electrode elements. Dielectric data were analyzed using complex electrical modulus M* at various temperatures. The modulus plots are characterized by the presence of two relaxation peaks thermally activated. The activation energies obtained from the analysis of M″ (0.90 eV) and conductivity data (0.94 eV) are very close, revealing an ionic hopping mechanism.  相似文献   

4.
A series of Ni and Ge co-doped manganese nitride materials were fabricated by mechanical ball milling followed by solid-state sintering. Their thermal expansion properties and electrical and thermal conductivities were investigated in the temperature range of 77–300 K. The results show that Ni and Ge co-doped manganese nitride materials have negative thermal expansion (NTE), and the operation-temperature window of NTE shifts toward the lower temperature region and the variation of linear thermal expansion (ΔL/L (300K)) in the operation-temperature window of NTE decreases with increasing Ni content. The combination of these two factors results in a low coefficient of thermal expansion (CTE) at cryogenic temperatures. The average CTE of Mn3(Cu0.2Ni0.4Ge0.4)N drops to ‘zero’ in the temperature range of 190–77 K. The values of electrical and thermal conductivities of the Ni and Ge co-doped manganese nitride materials are in the ranges of 2–3×103 (ohm cm)−1 and 1.6–3.4 W (m K)−1, respectively.  相似文献   

5.
Anomalies of the dielectric properties of undoped and aluminum-and gallium-doped crystals of Bi12SiO20 are investigated in the frequency and temperature range ν=102–108 Hz and T=300–800 K. They are shown to be due to Debye relaxation processes and determined by the relaxor parameters. The mechanism of electron thermal polarization is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1223–1229 (July 1997)  相似文献   

6.
R Bharati  R Shanker  R A Singh 《Pramana》1980,14(6):449-454
The temperature dependence of the electrical conductivity, thermoelectric power and dielectric constant of the antiferromagnetic CuWO4 have been studied in the temperature range 300–1000 K. The conductivity results can be summarised by the equations σI=6.31 × 10−3 exp (−0.29 eV/kT) ohm−1 cm−1 in the temperature range 300–600 K and σII=3.16 × 105 exp (−1.48 eV/kT) ohm−1 cm−1 between 600 K and 1000 K. The thermoelectric power can be expressed byθ=[− 1.25 (103/T) + 3.9] mV/K. Initially dielectric constant increases slowly but for high temperatures its increase is fast.  相似文献   

7.
We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa2Se4:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f6 5d–4f7 (8S7/2) of the Eu2+ ions. From the temperature dependence of the intensity (log I–103/T), we determined the activation energy (E a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu2+ ions in the CaGa2Se4 crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.  相似文献   

8.
The anisotropy of the optical properties of a single crystal of the hexagonal manganite HoMnO3 has been investigated by spectroscopic ellipsometry in the spectral range 0.6–5.0 eV. It has been demonstrated that the optical absorption edge for the polarization Ec is determined by the intense narrow transition O(2p) → Mn(3d) centered at 1.5 eV, whereas this transition for the polarization Ec is strongly suppressed and shifted toward higher energies by 0.2 eV. It has been revealed that, at the temperature T = 293 K, the spectra for both polarizations Ec and Ec exhibit a broad absorption band centered at ∼2.4 eV, which was earlier observed in nonlinear spectra during optical second harmonic generation.  相似文献   

9.
The electrical conductivity σ of crystals of lithium heptagermanate Li2Ge7O15 doped with Cr and Mn is measured in an alternating-current field with a frequency of 1 kHz in the temperature range 300–700 K. It is found that doping strongly affects the electrical conductivity. It is established that the addition of 0.1 wt % Cr leads to an increase in the electrical conductivity σ by almost one order of magnitude, whereas the introduction of 0.03 wt % Mn substantially reduces the electrical conductivity along particular crystallographic directions. Data available on the incorporation of Cr and Mn impurity atoms into the lattice suggests that the electrical conductivity is determined by lithium ions hopping over interstitial positions along the structural channels.  相似文献   

10.
The electrical and thermal conductivities of an YbInCu4 polycrystalline sample have been measured within the 4.2–300-K range. The behavior of the heat conductivity has been found to change sharply above and below T v =70–75 K, the temperature corresponding to an isostructural phase transition from a state with an integral valence (T>T v ) to a mixed-valence state (T<T v ) of Yb ions. A preliminary qualitative analysis of the results is presented. Fiz. Tverd. Tela (St. Petersburg) 41, 1548–1551 (September 1999)  相似文献   

11.
LiCoO2 thin films were prepared by electron beam evaporation technique using LiCoO2 target with Li/Co ratio 1.1 in an oxygen partial pressure of 5 × 10−4 mbar. The films prepared at substrate temperature T s < 573 K were amorphous in nature, and the films prepared at T s > 573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature range 673–773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co–eg absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co–t2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment exhibit (104) out plane texture with large grains. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006  相似文献   

12.
Three different photomagnetic effects caused by ultraviolet light in paramagnetic crystals based on molecules of spiropyrans (Sp) Sp3Cr(C2O4)3 and SpI have been revealed and separated: (1) in the high-temperature range (30–300 K), the photomagnetic effect in Sp3Cr(C2O4)3 is determined by the charge transfer between chromium ions and spiropyran molecules; (2) in the low-temperature range (2 K), the photomagnetic effect in Sp3Cr(C2O4)3 is due to the photoisomerization of spiropyran molecules, the change in the crystal field, and the splitting of the levels of Cr3+ ions in zero field; and (3) in the temperature range 2–20 K, the generation of radiation-induced paramagnetic defects contributes to the magnetic moment of the organic sublattice Sp+.  相似文献   

13.
《Solid State Ionics》1986,20(3):191-196
Ionic thermocurrent (ITC) in NaF thin film deposited between gold electrodes has been investigated in situ in the temperature region 300–500 K. The thermally stimulated polarization current (TSPC) and thermally stimulated depolarization current (TSDC) obtained under low electric field pf polarization (Ep) at a lower temperature of polarization (Tp) exhibited current-peak temperatures (TM) about 420 K and 450 K. The activation energies associated with the first and the second current peaks were 1.15 + 0.05 eV and 0.65 + 0.02 eV, which are assigned to cation vacancy blocking at the grain boundary barrier and the electrode contact interface barrier respectively. Polarization under a strong electric field (Ep > MV m−1) at Tp > 480 K causes a quasi-stable shift of the ITC peak positions to higher temperature. The current peak positions and magnitudes then depend upon the polarity of the electrode metal during polarization, and activation energies associated with the first peak positions are 0.90 + 0.02 eV and 0.79 + 0.02 eV for positive and negative bias at the counter electrode respectively, which may be attributed to the clustering of the cation vacancies and the dislocation networks at the interfaces.  相似文献   

14.
We have studied the spectral and kinetic characteristics of pulsed cathodoluminescence of feldspars (albite, microcline, amazonite) in the time range 10−8–10−2 sec and the temperature range 28–300 K. We have shown that the bands in the UV region of the spectrum (5.39, 4.35, and 3.75 eV) are due to intrinsic luminescence of the crystals. The ratio of the intensities of these bands characterizes the phase composition of the mineral: in the luminescence spectra of microcline, for all temperatures the 4.35 eV band dominates; in the pulsed cathodoluminescence spectra of albite, the bands at 3.75 eV (at 300 K) and 5.39 eV (at 28 K) dominate. The parameters of the luminescence decay kinetics for the impurity ions Fe3+ and Mn2+ are more sensitive to local perturbations of the lattice structure than the position of the emission band maximum, and can be an effective indicator of the origin of the mineral. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 339–343, May–June, 2006.  相似文献   

15.
Om Prakash  Ashok Rao  P N Dheer 《Pramana》1992,39(6):655-660
A dilatometer, using the three terminal capacitance technique, suitable for measurement of linear thermal expansion of solids in the temperature range 1.3–300 K is described. The dialtometer is designed such that the mounting system for the specimen does not undergo any significant changes in dimensions when the specimen is heated. The apparatus, therefore, yields in principle absolute values of α, the coefficient of linear thermal expansion. The performance of the apparatus has been checked by measurements on copper in the temperature range of 77–300 K. Some preliminary results on the behaviour of α for Y1Ba2Cu3O6.9 compound in the vicinity of superconducting transition temperature,T c are also described. The system can detect relative changes in length Δl/l 0 of about 10−8. Attempts are being made to improve the sensitivity.  相似文献   

16.
Summary The photoconductivity of the magnetic semiconductor compound Cd1−x Mn x Se has been studied at 300 K and at 77K for the first time for several Bridgman-grown single crystals. With this technique it was possible to detect the Mn 3d level. Experimental data found in this investigation reveal that the Mn 3d level is pinned at 1.9 eV below the bottom of the conduction band,i.e. it is independent of temperature and insensitive to the amount of manganese. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.  相似文献   

17.
The influence of the replacement of Mn ions in the La0.7Ca0.3Mn1 − y Fe y O3 compounds (0 ≤ y ≤ 0.09) by another transitional metal, Fe, was studied. The radii of both ions are almost identical, which makes the effect of the transitional metal on the physical properties of manganites more transparent. The crystal structure of three samples (with y = 0, 0.03, 0.09) is studied in the temperature range T = 1.5–300 K by neutron powder diffraction. All investigated samples belong to the orthorhombic space group Pnma (62). It is confirmed that Fe ions occupy the Mn positions in the unit cell. As the Fe concentration increases, the saturation value of the spontaneous magnetic moment and the Curie temperature decrease, but the ground state remains ferromagnetic for 0 ≤ y ≤ 0.1. The saturation values of the magnetic moments at T = 1.5 K are m FM = 3.72(3), 3.40(3), and 3.27(3) μ B /Mn for the samples with an Fe concentration y = 0, 0.03, and 0.09, respectively. Original Russian Text ? A.I. Kurbakov, V.S. Zakhvalinskii, R. Laiho, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 691–695.  相似文献   

18.
2 and Dy-doped p-TlGaSe2 (p-TlGaSe2:Dy)single crystals were grown by the Bridgman–Stockbarger method. Absorption spectra were measured on freshly cleaved (001) surfaces. The freshly cleaved crystals had a mirror-like surface and there was no need for mechanical treatment. The absorption measurements were carried out in p-TlGaSe2 and p-TlGaSe2:Dy samples in the temperature range 10–320 K with a step of 10 K. The phonon energies calculated in p-TlGaSe2 and p-TlGaSe2:Dy are 23.0 meV and 21.0 meV, respectively. The direct band gaps of p-TlGaSe2 and p-TlGaSe2:Dy are 2.279 eV and 2.294 eV at 10 K, respectively. There is an abrupt change for the energy peak for p-TlGaSe2 in the temperature ranges 105–120 K, 240–250 K, and for p-TlGaSe2:Dy in the temperature ranges 100–110 K, 240–260 K. Received: 3 December 1997 / Accepted: 5 October 1998  相似文献   

19.
The field (0–5.5 T) and temperature (2–300 K) dependences of the magnetization of LiTmF4 powders with particle sizes of 1 μm and 56–400 μm are investigated experimentally and theoretically. It is concluded that a transition layer exists between the thulium ions in the bulk and the ions at the surface. Two magnetic-field-induced structural phase transitions are observed at low temperatures, and the temperature dependence of the critical magnetic fields is established. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 247–250 (25 August 1997)  相似文献   

20.
An investigation was made of the influence of γ irradiation on the temperature dependences of internal friction in disk-shaped silicon substrates in the kilohertz frequency range. After exposure to doses of 104 and 105 R, two dominant internal friction peaks were observed at ∼330 and ∼450 K with activation energies H 1=0.6 eV and H 2=0.9 eV, respectively. These peaks were evidently caused by reorientation of interstitial silicon atoms in dumbbell configurations. Fiz. Tverd. Tela (St. Petersburg) 40, 1257–1258 (July 1998)  相似文献   

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