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1.
The observed anomalous decrease in the proton spin-lattice relaxation timeT 1 on approaching the Curie point in a rather pure KH2PO4 single crystal is explained by magnetic dipolar coupling to the ferroelectric mode. The isolated “non-interacting” O?H...O proton flipping time is estimated from theT 1 data as τ=0.66·10?12 sec for the paraelectric phase and τ=2.24·10?12 sec for the ferroelectric phase, in good agreement with the results obtained from other methods. 相似文献
2.
The specific heat of crystalline [NH2(CH3)2]2 · CuCl4 in the ferroelectric phase, both nonirradiated and irradiated by electrons, was measured calorimetrically. The temperature region of existence of the ferroelectric phase was shown to broaden under electron irradiation. The existence of an incommensurate phase above the Curie point T c1 in the crystal was confirmed. The phase-transition sequence observed in [NH2(CH3)2]2 · CuCl4 is shown to be described by a phenomenological model for A 2 BX 4-type ferroelectrics with an organic cation. 相似文献
3.
M. Zdanowska-Frączek Z.J. Frączek P. Szklarz R. Jakubas 《Journal of Physics and Chemistry of Solids》2012,73(7):953-956
The hydrostatic pressure effect on the dielectric properties of (NH4)2H2P2O6 ferroelectric crystal was studied for pressures from 0.1 MPa to 360 MPa and for temperatures from 100 to 190 K. The pressure–temperature phase diagram obtained is linear with increasing pressure. The paraelectric–ferroelectric phase transition temperature decreases with increasing pressure with the pressure coefficient dTc/dp=?5.16×10?2 K MPa?1. Additionally, the pressure dependences of Curie–Weiss constants for the crystal in paraelectric (C+) and ferroelectric (C?) phases are evaluated and discussed. The possible mechanism of paraelectric–ferroelectric phase transition is also discussed. 相似文献
4.
The dielectric properties of the [4-NH2C5H4NH] SbCl4 (abbreviated as 4-APCA) crystal were investigated under hydrostatic pressure up to 300 Mpa. The pressure-temperature phase diagram was given. The paraelectric-ferroelectric phase transition (II→III) temperature (Tc) increases linearly with increasing pressure with a slope dTc/dp=21×10−2 K/MPa. The pressure dependence of Curie-Weiss constants has been evaluated also. In the paraelectric phase (II) the Curie constant (C+) was pressure dependent whereas the C− constant over the ferroelectric phase (III) was almost constant. The results are interpreted in terms of improper and displacive type phase transition model with a soft phonon at a zone boundary. 相似文献
5.
The influence of bias and variable electric fields on the dielectric response of the K0.91(NH4)0.09H2PO4 single crystal has been studied in the vicinity of the ferroelectric phase transition temperature T C. Below T C, the nonlinear response is caused mainly by the domain mechanism. This is confirmed, in particular, by observations of chaotic oscillations in a series RLC-circuit containing the studied sample as a capacitor C and excited by a sinusoidal voltage. Peculiarities of the behavior of the dielectric nonlinearity are found near the Curie temperature, which are explained by the emergence of an intermediate heterophase state. 相似文献
6.
Crystals of the BaM2+F4 family are known to be ferroelectric with extra-polated Curie temperatures lying 100 K or less above their melting points. In the present Raman study the anomalous temperature dependences of frequency and intensity for one vibrational mode in BaZnF4 and BaMgF4 are correlated with dielectric properties. 相似文献
7.
Dielectric properties of lithium–sodium–tetragermanate (LNG) LiNaGe4O9 crystal were investigated under hydrostatic pressure. The phase diagram and phase transition temperature as a function of pressure was constructed. Up to 200 MPa the dependence of TC on pressure is linear with negative slope of 8.5 K/GPa. The influence of pressure on the Curie–Weiss law was observed. It was also shown that with increasing pressure the maximum value of the electric permittivity and Curie–Weiss constant are decreasing. The obtained results revealed complex mechanism of phase transition in the ferroelectric LNG. 相似文献
8.
The low-frequency internal friction Q ?1 and the shear modulus G in a paraelectric phase of CsH2AsO4, KD2PO4, and KH2PO4 ferroelectrics were studied using a reversed torsion pendulum method. Anomalies in the Q ?1(T) and G(T) dependences were observed above the Curie temperatures of these crystals, at temperatures 308, 253, and 293 K, respectively. The anomalies were associated with a first-order phase transition $(\bar 42m \to mm2)$ occurring in the foreign phase inclusions. 相似文献
9.
Using the standard solid-state reaction method, several vanadium-doped ferroelectric ceramics of type SrBi4−x/3Ti4−xVxO15 (SBTV−x) were synthesized. The vanadium doping content, x, rangs from 0.00 to 0.06. The crystal structure of SrBi4Ti4O15 is not affected by V-doping. The electric breakdown voltage of the samples increases with V content. Meanwhile, V-doping results in a notable enlargement of remnant polarization (2Pr). The 2Pr of STBV−0.03 reaches a very large value, which is over 50 μC/cm2 and is nearly twice greater than that at zero doping. The Curie temperatures of V-doped samples decrease slightly in comparison with that of SrBi4Ti4O15. V-doping can improve the electric properties of SrBi4Ti4O15 without sacrificing its thermal stableness. 相似文献
10.
Using the standard solid-state reaction method, several vanadium-doped ferroelectric ceramics of type SrBi4−x/3Ti4−xVxO15 (SBTV-x) were synthesized. The vanadium doping content, x, ranges from 0.000 to 0.06. The crystal structure of SrBi4Ti4O15 is not affected by V-doping. The electric breakdown voltage of the samples increases with V content. Meanwhile, V-doping results in a notable enlargement of remnant polarization (2Pr). The 2Pr of STBV-0.03 reaches a very large value, which is over 50 μC/cm2 and is nearly twice greater than that at zero doping. The Curie temperatures of V-doped samples decrease slightly in comparison with that of SrBi4Ti4O15. V-doping can improve the electric properties of SrBi4Ti4O15 without sacrificing its thermal stableness. 相似文献
11.
In this paper, effects of lead doping on the lattice response and phase transitions of Sr1−xPbxBi2Nb2O9 (x=0.0-0.5 in steps of 0.1) ferroelectric ceramics are reported. It is observed that structure attains more tetragonality with doping of lead up to 40%. Increased orthorhombic distortion is observed for undoped SBN and 50 at.% lead substituted SBN. Phase transitions for all samples were studied using Curie temperature measurements and are explained in terms of lattice response of these ceramics. Sample with x=0.5 shows decreased tetragonal strain and Curie temperature. Relationship of polarization with lattice response is discussed. 相似文献
12.
The antiferroelectric (Pb0.985Sm0.01) (Zr1-xTix)O3 (Ti-PSZO) thin films were synthesized on Pt(111)/Ti/SiO2/Si substrates using a chemical solution deposition method. The films were crystallized in the perovskite phase with a preferential orientation along (111) direction. With Ti doping in PSZO, a gradual transformation from antiferroelectric to ferroelectric phase transition was noticed at room temperature owing to the Ti doping induced lattice distortion. The phase transition has been confirmed through the P - E hysteresis loops, X-ray diffraction (peak shifting), capacitance-voltage measurements, and Raman scattering analysis. The thin film with Ti = 0.15 doping displayed a ferroelectric behavior with high dielectric constant and large dielectric tunability of about 62%. Also, Ti doping altered the Curie temperature (Tc) and enhanced the order of dielectric diffuseness. It is believed that Ti-doping in PSZO is an effective way to induce an antiferroelectric - ferroelectric phase transition and to tailor the electrical characteristics of PSZO thin films. 相似文献
13.
14.
Akhilesh Kumar Jain 《Solid State Communications》1979,31(4):237-239
From a reinterpretation of EPR results on γ-irradiated K2SeO4 crystals, previously reported by Aiki et al., the space group symmetry for commensurate (ferroelectric) phase of K2SeO4 is determined to be Pna21. The EPR results support the modulation of polarization as the reason for disappearance of ferroelectricity in incommensurate phase. 相似文献
15.
Ferroelectricity and phase transition from incommensurate phase into commensurate one in (NH4)2ZnCl4
I.A. Belobrova A.K. Moskalev N.V. Bizukina S.V. Milul I.P. Aleksandrova 《Solid State Communications》1980,33(11):1101-1102
Phase transition has been found in (NH4)2ZnCl4 at T = 266 ± 0.5 K by NQR method. There is a ferroelectric phase below Tc with a space group P21cn and with the trebling of the elementary lattice parameter along the axis c. Above the phase transition temperature in the crystal (NH4)2ZnCl4 an incommensurate phase is realized. 相似文献
16.
A. A. Sidorkin A. S. Sidorkin O. V. Rogazinskaya S. D. Milovidova 《Physics of the Solid State》2002,44(2):358-360
Thermally stimulated electron emission is experimentally observed in ferroelectric triglycine sulfate (TGS) crystals in a temperature range whose upper limit is 10–15 K above the Curie point. Samples of a nominally pure and a chromium-doped TGS crystal, heated at different constant rates q=dT/dt, are investigated. It is shown that an increase in the heating rate results in increased emission current density over the entire temperature range investigated. The temperature at which emission arises depends only slightly on the rate q. At the same time, the temperature at which emission ceases increases monotonically with increasing q; if q is less than 1 K/min, this temperature is below the Curie point, while at q=4–5 K/min, this temperature becomes as large as 60–65°C, which is more than 15°C above the Curie point. In chromium-doped TGS crystal, the electron emission onset temperature is close to that of pure TGS, but the width of the temperature range over which emission is observed in the paraelectric phase is approximately two times less than in the case of pure TGS heated at the same rate. The emission disappearance below the Curie point (in the ferroelectric phase) at low q is explained as a result of full emptying of the electron traps under slow heating. The reason for the occurrence of emission above the Curie point is related to the charges that shield the spontaneous polarization and, because of their slow relaxation, persists in the paraelectric phase. 相似文献
17.
V. V. Gorbatenko V. I. Kudriash B. N. Prasolov S. A. Gorbatenko 《Bulletin of the Russian Academy of Sciences: Physics》2013,77(8):1041-1046
Harmonic analysis of repolarization in A 2 BX 4-group crystals in the ferroelectric phase near phase-transition temperature T c is used to separate the contributions to the harmonic-component amplitudes in the output signal of a Sawyer-Tower circuit from charging the reference capacitor with capacitive and conductive current through such a crystal. Harmonic analysis of dielectric hysteresis loops obtained by placing a specimen in an electric field with harmonically changing strength reveals general regularities in the evolution of the domain walls of A 2 BX 4-group crystals. It is established that the domain structure affects the nonlinear polarization properties of our specimens. The dependence of the potential relief of ferroelectric ion motion in a harmonically changing electric field is plotted on the basis of the experimental results. 相似文献
18.
The heat capacity of [NH2(CH3)2]2 · CuCl4 crystals prior to and after γ-irradiation with doses of 1, 5, 10, and 50 MR is measured by the calorimetric method in the temperature range 80–300 K. It is found that, as the temperature decreases, the temperature dependence C p (T) exhibits two anomalies which correspond to phase transitions from the incommensurate to the ferroelectric phase at T c =281 K and from the ferroelectric to the ferroelastic phase at T 1=255 K. The nature of the anomalies is typical of a first-order phase transition. In addition, a smeared anomaly in the form of a small increase in the heat capacity of the ferroelectric phase is observed at T≈275 K. It is demonstrated that when the dose of γ-irradiation increases, the anomalies decrease in magnitude and the phase transition temperatures are displaced: T c increases and T 1 decreases. 相似文献
19.
Crystals of the (NH4)2SO4 ammonium sulfate are studied using x-ray diffractometry. It is revealed that the temperature dependence of the lattice parameters exhibits an anomalous behavior, namely, a global hysteresis, and an anomalous increase in the lattice parameter a and the unit cell volume at temperatures below the ferroelectric phase transition point (T c=223 K). The series of superstructure reflections observed corresponds to an incommensurate composite structure. Analysis of the temperature behavior of the mismatch parameters for the matrix (host) and superstructure (guest) lattices demonstrates that the (NH4)2SO4 compound undergoes a number of phase transitions, including a transition to a three-dimensionally incommensurate composite phase and transitions to commensurate (along one of the crystallographic directions) composite phases. 相似文献
20.
A. Levstik R. Blinc P. Kadaba S. Čižikov I. Levstik C. Filipič 《Solid State Communications》1975,16(12):1339-1341
Orthorhombic CsH2PO4 undergoes a ferroelectric transition at Tc = ?119.5°C, whereas the ferroelectric transition temperature in isomorphous CsD2PO4 is Tc = ?5.55°C. The transitions are of first order in both cases. The rather large isotope effect demonstrates the importance of the OHO bonds in the transition mechanism. 相似文献