首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Se58Ge42−x Pb x (9≤x≤20) glasses have been prepared using conventional melt quenching technique. Differential Scanning Calorimetric (DSC) measurements show single glass transition and double crystallization, which indicate the occurrence of phase separation in the samples. The phases present in the samples were identified using XRD. The kinetics of the glass transition has been studied in terms of the variation of glass transition temperature with composition and heating rate. In addition to this, activation energy of the glass transition (E t ) has also been evaluated and its composition dependence is also investigated. The thermal stability of these glasses has been investigated using various stability criteria: Deiztal first glass criterion, ΔT, Saad and Poulain weighted thermal stability, H′ and the S-parameter. The values of these parameters were obtained using various characteristic temperatures such as the glass transition temperature, T g , the onset temperature of crystallization, T c , and the peak crystallization temperature, T p . The values of stability parameters show that the phase corresponding to second crystallization is more stable than the phase corresponding to first one. The stability in terms of the lead (Pb) content has been determined considering the values of stability parameters of the phase corresponding to second peak. It was found that the stability increases with the lead content.  相似文献   

2.
X-ray powder diffraction (XRD) and magnetic measurements were performed in order to investigate the effect of Na+ ion substitution for Ca2+ ions on the crystallographic structure, the character of magnetic ordering, and the effect of transition temperature in La0.7Ca0.3−x Na x MnO3 manganites series (0 ⩽ × ⩽ 0.2). All samples crystallise in an orthorhombic structure with the Pnma space group. We have found a strong dependence of structural and magnetic properties on the cation-size disorder parameter σ 2. The temperature dependence of magnetization of all samples obeys the Bloch T 3/2 law. The values of the spin wave constant at low temperature B increase with the increase of x and the Curie temperature decreases. It is concluded that the substitution of Ca by Na+ ions causes a decrease in total exchange integral Aof the samples.   相似文献   

3.
Resonant absorption of microwaves in CuGeO3 single crystals in a frequency band of 40 to 120 GHz, in magnetic field B⩽15 T, at temperatures ranging between 0.5 and 300 K, and in the configuration Ba has been investigated. Several absorption lines (S 0, S a, and S b) whose parameters strongly depend on temperature have been detected close to ESR. The temperature dependence of the total absorption in the main line S 0 with the Landé g-factor g 0=2.154 at temperatures above the spin-Peierls transition temperature is in good agreement with Bonner and Fisher’s theoretical prediction for a one-dimensional Heisenberg spin chain. In addition to the main resonance, a resonance of smaller amplitude, S a, with the g-factor g a=2.72 has been detected at temperatures ranging down to a characteristic temperature T≃1 K, below which the amplitude of this feature drops to zero. A radical restructuring of the magnetoabsorption spectrum occurs at the temperature of the spin-Peierls transition T SP≈14 K. At T<12 K new features emerge in the spectrum, namely, a broad absorption line overlapping with the narrow lines S 0 and S a, and a line S b with g b=1.83, which is not detected at temperatures above T SP. An analysis of amplitudes and total absorption of ESR lines as functions of temperature has shown that the temperature range below 1 K is anomalous, which may be caused by an additional ordering in the CuGeO3 magnetic subsystem at low temperatures. Zh. éksp. Teor. Fiz. 112, 1727–1738 (November 1997)  相似文献   

4.
N. N. Efimova 《JETP Letters》1998,67(5):346-351
It is established on the basis of an investigation of the temperature dependences of the saturation magnetization σS(T) and the magnetic contribution to the specific heat C m(T) that in the reentrant region of the x-T diagram (0.9⩽x⩽1.5) of dilute iron spinels Li0.5Fe2.5− x GaxO4 there exists between the line of Curie points T C(x) and the line of freezing temperatures T f(x) another line of first-order phase transitions T 1(x) to a noncollinear ferrimagnetic phase: T C(x)⩽T 1(x)⩽T f(x). Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 329–333 (10 March 1998)  相似文献   

5.
Reentrant behavior to a spin glass state is discovered in the solid solution system CuCr1.5+0.5x Sb x0.5−0.5 x S 4 with x=0.34 and 0.4. The spin-glass transition temperature T f determined from the kink in the temperature dependence of the initial susceptibility in an alternating magnetic field depends on the measurement frequency ω. It is shown that the frequency dependence T f (ω) is a power-law function 1/ω=(1/ω0)[T f /( T f T *)]zv with zv =7.7 for both compositions. For the composition with x =0.34 a maximum is observed near T * in the temperature dependence of the resistivity. These facts indicate that the transition from the spin glass to long-range magnetic order is a phase transition. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 265–269 (25 August 1996)  相似文献   

6.
xSb2O3-40TeO2-(60 − x) V2O5 glasses with 0 ≤ x ≤ 10 (in mol%) have been prepared by rapid- melt quenching method. DSC curves of these ternary glasses have been investigated. The glass transition properties that have been measured and reported in this paper, include the glass transition temperature (T g ), glass transition width (ΔT g ), heat capacity change at glass transition (ΔC P ) and fragility (F). Thermal stability, Poisson’s ratio, fragility and glass forming tendency of these glasses have been estimated, to determine relationship between chemical composition and the thermal stability or to interpret the structure of glass. In addition, Makishima and Makenzie’s theory was applied for determination of Young’s modulus, bulk modulus and shear modulus, indicating a strong relation between elastic properties and structure of glass. Generally, results of this work show that glass with x = 0 has the highest shear, bulk and Young’s moduli which make it as suitable candidate for the manufacture of strong glass fibers in technological applications; but it should be mentioned that glass with x = 8 has higher handling temperature and super resistance against thermal attack.  相似文献   

7.
The compositional dependence of thermal properties, such as glass transition temperature (Tg), non-reversing enthalpy change (ΔHNR) and the specific heat capacity change (ΔCp) of melt quenched Ge7Se93-xSbx (21 ≤ x ≤ 31) glasses, has been studied using alternating differential scanning calorimetry (ADSC) which is analogous to modulated differential scanning calorimetry (MDSC). The glass transition temperature, Tg, which is a measure of global connectivity of the glass, has been found to increase with the addition of Sb. In addition, a change in slope has been observed in the composition dependence of Tg at an average coordination 〈r〉 = 2.40. The experimentally observed compositional variation of glass transition temperature, has been compared with the theoretical predictions from the stochastic agglomeration theory (SAT) and has been found to be consistent. Further, a narrow thermally reversing window is seen in the compositional variation of the relaxation enthalpy (ΔHNR), which is centered around 〈r〉 = 2.40. The change in specific heat capacity (ΔCp) at Tg is also found to exhibit a distinct minima at 〈r〉 = 2.40, suggesting that the structural rearrangements for the liquid in the glass transition region are minimized around 〈r〉 = 2.4.  相似文献   

8.
H. Kumar  N. Chandel 《Phase Transitions》2016,89(11):1103-1118
In this communication, we report the results of calorimetric measurements on the samples of recently synthesized multi-component glassy alloys of Se78?xTe20Sn2Bix (0 ≤ x ≤ 6) system. For calorimetric study of glass transition kinetics, differential scanning calorimetry (DSC) technique has been used in non-isothermal mode. Peak glass transition temperature (Tg) is determined using the DSC scans. Kinetic parameters A and B of glass transition are determined using heating rate dependence of Tg. Activation energy of glass transition (Eg) has been calculated using Moynihan and Kissinger methods. Glass-forming ability and thermal stability are also determined using Hurby and Saad–Poulin relations, respectively.  相似文献   

9.
From light-scattering studies on polybutylmethacrylate, a polymeric glass, the variation of the velocity and attenuation of thermally excited hypersonic phonons with temperature has been measured. Measurement of the temperature dependence of the ratio of the intensity of the Rayleigh line to the Brillouin lines is interpreted as due to a configurational rearrangement within the glass above the glass transition temperature, Tg . Only light scattered from longitudinal phonons was observed. The distinct change in the temperature dependence of the velocity, attenuation and intensity ratio identified the glass transition.

For samples annealed well above Tg, Tg was found to be about 0°C from the light-scattering studies, 12°C from differential scanning calorimetry (DSC), and 20°C from refractive index measurements. For an unannealed sample the behaviour of the above parameters with temperature was found to be different. Tg for the unannealed sample was 14°C from light-scattering, 18°C from DSC and 20°C from index of refraction measurements.  相似文献   

10.
The glass transition temperature dependence to heating rate and therefore the activation energy (ΔH?) of the glass transition of (60-x)V2O5xNiO–40TeO2 oxide glasses with 0≤x≤20 (in mol%) were investigated at heating rates φ (=3 6, 9, 10 and 12 K/min) using differential scanning calorimetry (DSC). The heating rate dependence of Tg was used to investigate the applicability of different theoretical models describing the glass transition. Using the application of Moynihan and Kissinger et al. models to the present data, different values of (ΔH?) at each different heating-rate regions were obtained. The fragility parameter (mH?/R Tg) was ∼24.98 for x=10 mol%, suggesting that this glass may be considered as a rather strong glass (fragility index m∼>20 is an indication of fragile glass). Also the compositional dependence of Tg and ΔH? was investigated.  相似文献   

11.
Solid solutions of the system La1−x CaxMnO3 are synthesized, and their magnetic and electrical properties are investigated. As x is increased, the crystal lattice changes symmetrically from an orthorhombic (x=0 and x=0.8) to a cubic structure (0<x⩽0.6 and x=1). Nonstoichiometric LaMnO3 and compositions with a low Ca content (0<x<0.4) are collinear ferromagnets. A metal-insulator transition is observed in them near the Curie temperature. Compositions with 0.6⩽x⩽0.9 exhibit a semiconductor-type conductivity and an unusual temperature behavior of the magnetization and the susceptibility with very distinct Curie and Néel temperatures. The magnetic properties of the solid solutions are explained on the basis of the model of ferro-antiferromagnetic phase separation. Zh. éksp. Teor. Fiz. 116, 1664–1675 (November 1999)  相似文献   

12.
In connection with the problem of identifying magnetic states in the vicinity of x 0 (the multicritical point of the x-T diagrams of spin-glass systems) a study has been made of properties that can be exploited to determine the presence of a thermodynamic phase transition at the Curie point T C and the distinctive features of the transition, specifically, the temperature dependence of the magnetic part of the specific heat C m(T), the temperature dependence of the low-field magnetization σ H(T), and (with a view toward examining critical behavior in a magnetic field) the magnetization isotherms σ H(T). The investigated object is the system of dilute ferrimagnetic spinels Li0.5Fe2.5−x GaxO4, in which every type of magnetic state has spatially inhomogeneous cluster structures. The results obtained for a sample with x=1.45 indicate that the classical criteria of a ferrimagnetic second-order phase transition at T C=(97±2) K occur for xx 0. The results of similar investigations for a sample with x=1.6, which exists in the cluster spin-glass state for T<T f=22 K and in an uncorrelated cluster state of the superparamagnetic type for T>T f, are also given for comparison with the preceding case. Zh. éksp. Teor. Fiz. 114, 2065–2077 (December 1998)  相似文献   

13.
A systematic μSR study of the local magnetic field distribution in a series of oxygen deficient YBa2Cu3O x samples with 6.5⩽x⩽7.0 is reported. Special attention was given to perform the experiments under the same conditions, so that the oxygen content of the measured samples was the only parameter varied. The behavior of the depolarization rate σ as a function of the oxygen contentx was found to have strong similarities with the behavior of the critical temperatureT c as a function ofx. In particular, two step-like increases of σ were observed abovex=6.7 and 6.9. The temperature dependence of the normalized depolarization rate σ(T)/σ(0) is well described by the two-fluid model forx⩾6.781(1) and clearly deviates from this behavior forx⩽6.704(1). Our results are compared to those obtained by other groups.  相似文献   

14.
The electrical resistance across the Cu-O layers of a BSCCO-2212 single crystal is investigated in the range of angles 0°⩽φ⩽90° between the magnetic field H⩽15 T and the ab plane. It is found that the temperature dependence R(T) at the transition into the mixed state is much sharper for φ≃0° than for 1°≲φ≲90°, where R is determined by the perpendicular component of the magnetic field and is described by the Arrhenius law R∼exp(−U/T). For H∥ ab hysteretic jumps in R(T, H), which vanish as the current increases, are observed at fields in the range 5.5⩽H⩽11 T. This effect can be attributed to a commensurate phase transition in a lattice of Josephson vortices. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 123–128 (25 January 1996)  相似文献   

15.
Explicit expressions have been derived for the volume dependence of electron-phonon coupling strength (λ) and the Coulomb pseudopotential (μ*) considering the variation of Fermi momentum (κ F) and Debye temperature (θ D) with volume. Ashcroft’s model pseudopotential and RPA form of dielectric screening have been used for obtaining pressure dependence of transition temperature (T C) and the logarithmic volume derivative (Φ) of the effective interaction strength (N 0 V) for metallic glass superconductor Mg70Zn30. It has been observed that T C of the metallic glass Mg70Zn30 decreases rapidly with increase of pressure and the superconducting phase disappears at about 30% decrease of volume, for which the μ* curve shows a minimum and an elbow is formed in the Φ graph.  相似文献   

16.
Bulk amorphous samples of Te-substituted Sn10Sb20Se70−X Te X (0≤X≤12) were prepared using a melt quenching technique. Calorimetric studies of the samples were performed using differential scanning calorimetry (DSC) and the glass transition temperature and crystallization temperature were evaluated from DSC scans. The glass transition temperature T g exhibits a sharp decrease for small Te substitution of X=2, thereafter increases with increase in Te content up to X=10, and then decreases for further Te substitution. The apparent activation energy for glass transition and the activation energy for crystallization were calculated using Kissinger, modified Kissinger, and Matusita equations. The change in glass transition temperature T g has been explained based on the bond formation energy of different heteropolar bonds. The optical band gap of thermally evaporated thin films of Sn10Sb20Se70−X Te X (0≤X≤12) was calculated from reflectance and transmittance data. The optical band gap variation with tellurium content exhibits a sharp decrease for an initial tellurium substitution of X=2 similar to that of the glass transition temperature and thereafter a peak is observed in optical band gap around X=4 composition.  相似文献   

17.
Differential scanning calorimetry (DSC) has been employed to investigate the glass transition activation energy E g, thermal stability and glass-forming ability (GFA) of Se90In10? x Sb x (x = 0, 2, 4, 6, 8, 10) chalcogenide glasses. DSC runs were performed at six different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperature. The dependence of glass transition temperature T g on heating rate (α), as well as composition of Sb, has been studied. From the dependence of glass transition temperature on heating rate, the E g has been calculated on the basis of the Kissinger [Anal. Chem. 29 (1957) p.1702] and Moynihan [J. Phys. Chem. 78 (1974) p.267] models. Thermal stability has been monitored through the calculation of temperature differences T cT g, the stability parameter S, and the enthalpy released during crystallization H c. The GFA has been investigated on the basis of the Hruby parameter H r, which is strong indicator of GFA. Results for GFA are in good agreement with fragility index F i calculations, indicating that Se90In6Sb4 is an excellent glass-former.  相似文献   

18.
The glass transition temperature and the dynamics of the α-process have been investigated using dielectric relaxation spectroscopy for single and stacked thin films of poly(2-chlorostyrene) (P2CS). The stacked film consists of 10 layers of single thin films with thickness of 12 nm or 18 nm. The glass transition temperature T g of the single thin films of P2CS is found to decrease with decreasing film thickness in a similar way as observed for polystyrene thin films. The magnitude of the depression of T g for the stacked thin films is larger than that of the single thin films with corresponding thickness. The depression of the temperature at which the dielectric loss shows a peak due to the α-process at a given frequency, T α, is larger than that of the single thin films, although the magnitude is smaller than that of T g . Annealing at a high temperature could cause the T g and T α of the stacked thin films to approach the values of the bulk system.  相似文献   

19.
By means of molecular-dynamics simulation we study a flexible and a semiflexible bead-spring model for a polymer melt on cooling through the glass transition. Results for the glass transition temperature T g and for the elastic properties of the glassy state are presented. We find that T g increases with chain length N and is for all N larger for the semiflexible model. The N dependence of T g is compared to experimental results from the literature. Furthermore, we characterize the polymer glass below T g via its elastic properties, i.e., via the Lamé coefficients λ and μ. The Lamé coefficients are determined from the fluctuation formalism which allows to split λ and μ into affine (Born term) and nonaffine (fluctuation term) contributions. We find that the fluctuation term represents a substantial correction to the Born term. Since the Born terms for λ and μ are identical, the fluctuation terms are responsible for the different temperature dependence of the Lamé coefficients. While λ decreases linearly on approaching T g from below, the shear modulus μ displays a much stronger decrease near T g. From the present simulation data it is not possible to decide whether μ takes a finite value at T g, as would be expected from mode-coupling theory, or vanishes continuously, as suggested by recent work from replica theory.  相似文献   

20.
Mössbauer spectroscopy has been performed in CdCr2xIn2–2xS4 spinel solid solutions (0.7x0.95). For x>0.85, reentrant properties are observed: For Tc, finite clusters occurs, decoupled of the ferromagnetic matrix; at low temperature, the ferromagnetic order seems to vanish and a spin glass state occurs. For x0.85, a spin glass state is observed and the properties are coherent rather with a phase transition.On leave of Tata Inst., Bombay 400005 INDIA  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号