共查询到20条相似文献,搜索用时 31 毫秒
1.
Proton and phosphorus spin-lattice relaxation time (T1) measurements were applied to study the antiferroelectric phase transition in betaine phosphate (CH3)3NCH2COO·H3PO4 at 86 K. In the whole temperature range studied, the T1 or 1H was governed by a dipolar fluctuation caused by the methyl- and the whole butyl-group reorientations. In the vicinity of the phase transition the T1 of 31P shows a sharp dip which is a characteristic of critical slowing down. The analysis of the T1 based on the order-disorder mechanism with respect to the position of the acidic protons leads to the critical exponent for the correlation length v=0.5. 相似文献
2.
G. A. Smolensky N. N. Kolpakova S. A. Kizhaev A. F. Ioffe 《Ferroelectrics Letters Section》1982,44(5):129-134
Raman scattering and electric permittivity of Cd2Nb2O7 were studied between 4 and 230 K. Phase transitions at T6 = 44 K and T7 = 19 K have been discovered. It is hggested that T6 = 80 K and T = 44 K correspond to normal-incohmensurate and ihcommensurate-commensurate phase transition points respectively. 相似文献
3.
Raman scattering of NH4SeO4 was investigated in the region of 0-1000 cm-1 at phase transitions between 70 and 296 K. It was observed that at T2, T3, T4, T5 the intensity of Raman lines and its temperature dependence changed. It is suggested that between T5 = 98 K and 296 K triclinic deformation of the lattice is delicate and below T5 the unit cell belongs to the space group P1. 相似文献
4.
George A. Rossett Jr. K. R. Udayakumar Michael J. Haun L. Eric Cross 《Journal of the American Ceramic Society》1990,73(11):3334-3338
A phenomenological free-energy function including the effects of elastic boundary conditions was presented and used to investigate the single-domain, single-crystal properties of the ferroelectric perovskite, PbTiO3 . In particular, the effects of tensile and compressive hydrostatic stress on the spontaneous polarization, Curie point, dielectric susceptibility, and piezoelectric property coefficients were examined. The calculated shift of the Curie point with hydrostatic stress, along with the entropy and enthalpy of the ferroelectric-paraelectric phase transition, was found to be in good agreement with experimental measurements. The isothermal variation of the relative dielectric susceptibility and piezoelectric coefficients with hydrostatic stress exhibited the expected behavior near the ferroelectric-paraelectric phase transition. 相似文献
5.
Dielectric permittivity along the [111] direction has been measured as a function of temperature for a relaxor ferroelectric single crystal (PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33 (PMN-33%PT). A sharp ferroelectric phase transition was observed near 425 K and 429 K for cooling and heating processes, respectively. As temperature decreases, a diffuse phase transition (which begins near 330 K upon cooling) was detected. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 330 and 425 K upon cooling) are diffuse first-order and first-order, respectively. The frequency-dependent dielectric data ε'111 (ƒ, T) prove the existence of an electric dipolar relaxation process between 350 and 400 K. The activation energy, the Vogel-Fulcher temperature and attempt frequency corresponding to this relaxation process are also calculated. 相似文献
6.
A. J. EASTEAL J. A. WILDER R. K. MOHR C. T. MOYNIHAN 《Journal of the American Ceramic Society》1977,60(3-4):134-138
The evolution of enthalpy of As2 Se3 glass during structural relaxation in the glass transition region was measured via differential scanning calorimetry for two types of time-temperature programs: rate-heating at 10 K/min following a cool at a constant rate (-20 to -0.31 K/min) and isothermal annealing following a temperature step from an equilibrium state. The rate-heating data yield kinetic parameters for the structural relaxation which predict accurately the evolution of the enthalpy during isothermal annealing. The glass heat capacities were independent of cooling rate within experimental precision (≤0.2%). In this respect, As2 Se3 is unlike previously studied glasses whose heat capacities are more dependent on thermal history. 相似文献
7.
The defect structure in 3 mol% Y-TZP was studied by correlated internal friction, dielectric loss, and ionic conductivity experiments. A prominent mechanical and dielectric loss peak occurs in the temperature range between 380 and 550 K that depends on the frequency of measurement. The relaxation parameters were determined as Hm = 90 ± 3 kJ·mol−1 , τ∞ = (1.0+1.5 −0.6 ) × 10−14 s for the mechanical relaxation and Hd = 84 ± 3 kJ·mol−1 , τ∞ = (1.6+1.7 −0.9 ) × 10–13 s for the dielectric relaxation. The ionic conductivity below 790 K is controlled by an activation enthalpy of H σ = 89 ± 3 kJ·mol−1 ; at higher temperatures H σ = 60 ± 3 kJ·mol–1 . An atomistic model is presented which assumes that oxygen vacancies are trapped by yttrium ions forming anisotropic complexes which—by reorientation—cause anelastic and dielectric relaxation. At higher temperatures (>790 K) these complexes are dissociated, which leads to the reduced activation enthalpy for ionic conductivity. 相似文献
8.
James F. Scott Ratnakar Palai Ashok Kumar Manoj K. Singh Nishit M. Murari Naba K. Karan Ram S. Katiyar 《Journal of the American Ceramic Society》2008,91(6):1762-1768
This paper reports on two new aspects of oxide perovskites: the first part is devoted to new phase transitions, especially at high temperatures; multiferroics such as BiFeO3 and Pb–Fe–W–titanate are emphasized but nonmagnetic materials such as SrSnO3 are included. The work summarized on bismuth ferrite emphasizes its metal–insulator transition near 1200 K (atmospheric pressure) and 47 GPa (room temperature); that on SrSnO3 emphasizes order–disorder phase transitions; and that on lead–iron tungstate–titanate exhibits a classic second-order ferroelectric phase transition, of which rather few are known in the literature. The second part of the paper presents a discussion of constant phase elements for oxide perovskite ceramics; this is a modern way of characterizing their dielectric relaxation, particularly near phase transition temperatures. 相似文献
9.
A. I. Baranov V. A. Sandler L. A. Shuvalov R. M. Fedosyuk 《Ferroelectrics Letters Section》1986,5(4):119-123
Ferroelectric phase transition was detected in monoclinic RbD2 PO4 at TC3 =313K in addition to the known antiferroelectric phase transition at TC2 =319K. The almost saturated value of the spontaneous polarisation is about Psy = 6.10-4 μC/cm2 at 280K. 相似文献
10.
Wuyi Pan Qiming Zhang Amar S. Bhalla Leslie E. Cross 《Journal of the American Ceramic Society》1988,71(6):302-C
The electric-field-induced strain in single-crystal BaTiO3 was investigated. For crystals relatively free of twinning, a longitudinal strain of 0.35% can be induced just above the ferroelectric-paraelectric phase transition temperature (Tc1 ) primarily by field-forced paraelectric-ferroelectric phase transition. For heavily twinned crystals, 90° domain reorientation under the applied electric field plays an important role in the induced strain below Tc1 , and an induced strain of 0.6% is observed a few degrees below Tc1 . Above Tc1 , the electrostrictive property measured by a weak excitation field is purely intrinsic. When the excitation field is large, so that a field-forced paraelectric-ferroelectric phase transition is involved, the x33 /P2 3 value (where x33 and P3 are the induced strain and polarization along the z axis, respectively) is intrinsic at higher temperature, but may be modified at temperatures just at and slightly above Tc1 by residual 90° twin structure. 相似文献
11.
G. GOODMAN 《Journal of the American Ceramic Society》1960,43(2):105-113
An unusual type of ferroelectric behavior has been observed in barium zirconium metaniobate, BaNb1.5 Zr0.25 O5.25 . The orthorhombic, pseudotetragonal single crystal displays dielectric hysteresis only in its c direction, with normal dielectric properties in the a-b plane. No evidence of a fist- or second-order ferroelectric-paraelectric transition has been observed up to 1400°C. The crystal melts incongruently at about 1525°C. A maximum in the dielectric constant occurs at 80°C. when measured at 103 c.p.s. but is not accompanied by any effect in the spontaneous polarization. The temperature of this k' maximum has the frequency dependence of a dielectric relaxation process with an average activation energy of 0.2 e.v. These properties are consistent with the idea of a higher than second-order ferroelectric-paraelectric transition in this material. The dielectric behavior is explicable in terms of 180°"dipole aggregates" having a wide range of activation energies of reversal. There are suggestions in the technical literature of similar behavior in other materials. 相似文献
12.
Paula M. Vilarinho Liqin Zhou Manfred Pöckl Nelson Marques João L. Baptista 《Journal of the American Ceramic Society》2000,83(5):1149-1152
The dielectric properties of (1− x )Pb(Fe2/3 W1/3 )O3 · x PbTiO3 solid solutions were investigated from 102 to 106 Hz in the temperature range 150–600 K. The phase transition of Pb(Fe2/3 W1/3 )O3 (PFW) was shifted by PbTiO3 (PT) additions to higher temperatures at a rate of 6.3 K/mol% of PT. The temperature dependence of dielectric permittivity showed a sharper transition as the PT content increased. Dielectric measurements in a wide temperature range showed the presence of a second set of dielectric peaks at higher temperatures (350–600 K), besides the ferroelectric–paraelectric phase transition. This second set of peaks vanished when the samples were annealed in nitrogen. The activation energy values for the second relaxation varied between 0.50 and 0.63 eV, in agreement with the conduction activation energy determined for each sample. This relaxation is apparently related to electron holes. 相似文献
13.
I. N. Flerov I. M. Iskornev H. V. Gorev L. V. Kirensky 《Ferroelectrics Letters Section》1983,44(8):235-239
The specific heat of pseudoproper ferroelectric-ferroelastic CsLiWO4 was measured in the temperature range from 90 to 305 K. The enthalpy and entropy changes at phase transitions were determined. Interpretation of the data associated with the transition Go → G1 is done in terms of the thermodynamical theory. 相似文献
14.
Kazuya Aida Yasuhiko Benino Vesselin Dimitrov Takayuki Komatsu Ryuji Sato 《Journal of the American Ceramic Society》2000,83(5):1192-1198
The kinetics of enthalpy relaxation (recovery) at the glass transition in x K2 O·(20− x )MgO·80TeO2 glasses has been examined from heat capacity measurements using differential scanning calorimetry to clarify the features of the structural relaxation in ternary TeO2 -based glasses. Ternary glasses such as 10K2 O·10MgO·80TeO2 show high thermal resistance against crystallization compared with binary glasses. The degree of fragility m estimated from the activation energy for viscous flow E η and the glass transition temperature T g is m = 55–62, indicating a fragile character in TeO2 -based glasses. Large heat capacity changes of 43.1–48.2 J·mol−1 ·K−1 are also observed at the glass transition. The activation energy for enthalpy relaxation Δ H is evaluated from the cooling rate dependence of the limiting fictive temperature, and values of Δ H = 897–1268 kJ·mol−1 are obtained. Negative deviation from additivity in Δ H is also observed. Values of the Kovacs–Aklonis–Huchinson–Ramos (KAHR) parameter θ estimated from Δ H and T g are 0.33–0.42 K−1 . It has been proposed that ternary glasses have more homogeneous and constrained glass structure compared with binary glasses. 相似文献
15.
Electric modulus formalism was used to study relaxation processes in the 0.75-mol%-La2 O3 -doped CeO2 system between 387 and 470 K in the frequency range 5 to 107 Hz. Two relaxation processes were observed in the isothermal studies: one at low frequencies due to long-range migration of free oxygen vacancies (process A) and one at high frequencies due to charge reorientation relaxation of (LaCe Vo 'defect associates (process B). The relaxation processes were analyzed using a nonexponential decay function (φ(t) = exp[—(t/τo β] for 0<β1) of the electric field. The activation enthalpy estimated for process A is 0.72 eV and for process B is 0.55 eV. 相似文献
16.
Dielectric measurements and X-ray diffraction studies were made in the system BaTiO3 -BaHfO3 for polycrystalline specimens containing from 0 to 30 mole % BaHfO3 . The maximum in the dielectric constant for each composition in creased as the BaHfO3 concentration was in creased to 16 mole % and then decreased with further BaHfO3 additions. Room-temperature lattice constants and hysteresis loops were meas ured for all compositions. A partial solid-state phase diagram is suggested for the solid solution area of the system. The phase diagram and the dielectric behavior of the system up to 16 mole % BaHfO3 are explained on the basis of Devonshire's thermodynamic theory. The ferroelectric-paraelectric transition in the composition containing 16 mole % BaHfO3 was essentially of second order and occurred between a ferroelectric rhombohedral phase and a paraelectric cubic phase. 相似文献
17.
Experimental investigations of the glassy dielectric absorption maximum at low temperatures between 10 K ≤ TM ≤ 100 K at 14 different ferroelectrics are presented. From these investigations one can conclude that a connection between localized states, which cause this absorption maximum, and the structural phase transition ferroelectric-paraelectric exists. 相似文献
18.
由N, N-二甲基乙酰胺、氯化胆碱、乙二醇或丙三醇以不同的摩尔比(1:1:3, 1:1:4)合成了一系列三元低共熔离子液体(nDMA:nCC:nethylene glycol=1:1:3, 1:1:4, nDMA:nCC:nglycerol=1:1:3, 1:1:4)。在293.15~323.15 K温度下, 间隔10℃, 0~600.0 kPa压力范围内, 用等温饱和法测量了CO2在三元体系中的溶解度。CO2在体系中的溶解度随压力增大呈线性增大趋势, 随温度升高而减小。计算了亨利常数, 结果表明, CO2在由N, N-二甲基乙酰胺, 氯化胆碱, 乙二醇以摩尔比1:1:3合成的三元体系, 温度为293.15 K下, 亨利常数最小, 最小值为2.174 MPa·kg·mol-1。报道了关于CO2吸收的热动力学性质, 包括焓变、熵变、Gibbs自由能变。其中, 焓变为负值, 说明此吸收为放热过程。 相似文献
19.
MARY ANN DEBOLT ALLAN J. EASTEAL P. B. MACEDO CORNELIUS T. MOYNIHAN 《Journal of the American Ceramic Society》1976,59(1-2):16-21
A method was developed to determine the kinetic parameters controlling structural relaxation in the glass transition region from data acquired during continuous heating or cooling. The nonexponential character of the relaxation is accounted for by assuming an equilibrium isothermal relaxation function of the form exp [−( t /Toe ) ß ], where Toe is a relaxation time and 0< β 1. The data are linearized using the method of Narayanaswamy, and the continuous temperature variation during heating or cooling is dealt with by invoking the superposition principle. The analysis yields the kinetic parameters A , the relaxation-time preexponential term; Δ h ★ , the relaxation-time activation enthalpy; x , a term describing the relative effects of temperature and structure on the rate of relaxation; and β. The method was applied to analysis of the variation of the enthalpy of vitreous B2 O3 during rate heating through the transition region following rate cooling through the same region at a variety of rates. 相似文献
20.
Ikuo Yanase Hidehiko Kobayashi Yoshio Shibasaki Takashi Mitamura 《Journal of the American Ceramic Society》1997,80(10):2693-2695
The tetragonal-to-cubic structural phase transition in pollucite (CsAlSi2 O6 ) was investigated using low-temperature X-ray powder diffraction in the temperature range of 93 to 298 K, and the lattice constants were refined with Rietveld analysis. It was found that CsAlSi2 O6 had a tetragonal phase with a space group of I 41 /acd in the temperature range of 93 to 248 K, a = 1.36337(4) nm, c = 1.36988(6) nm at 248 K, and underwent a phase transition from tetragonal to cubic with a space group of Ia-3 in the temperature range of 248 to 273 K, a = 1.36645(3) nm at 273 K. 相似文献