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1.
Wojciech Medycki 《Solid state nuclear magnetic resonance》1999,13(4):213-218
Spin-lattice relaxation times T1 and T1ρ are determined for protons in three polycrystals (CH3NH3)5Bi2Cl11, (CD3NH3)5Bi2Cl11 and (CH3ND3)5Bi2Cl11. The temperature dependencies of the relaxation times obtained for (CH3NH3)5Bi2Cl11 and (CD3NH3)5Bi2Cl11 are interpreted as a result of correlated motions of the three-proton groups of the monomethylammonium cation. The minimum of the T1ρ relaxation time is explained as a result of the oscillations of the symmetry axis of the whole cation. 相似文献
2.
Effect of glycine substitution on the ferroelectric phase of betaine arsenate [(CH3)3NCH2COO·H3AsO4]
The present work reports an experimental investigation on the influence of glycine (NH2CH2COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate, (CH3)3NCH2COO·H3AsO4. The dielectric dispersion (20 Hz<ν<3 MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130 K<T<100 K). The results obtained for a single crystal with nominal glycine content of 20% are analyzed, compared with those obtained for pure betaine arsenate and discussed within the scope of a phenomenological Landau model previously used to describe a system with competing ferroelectric and structural instabilities. 相似文献
3.
The absorption spectra of the [NH2(C2H5)2]2CuCl4 crystals grown from a solution in ethyl alcohol and also of solid solutions of [NH2(C2H5)2]2Zn0.5Cu0.5Cl4 in the visible spectral region have been investigated in the vicinity of thermochromic phase transitions. It is shown that the phenomenon of thermochromism in these crystalline compounds is primarily related to the replacement of the square-planar geometry of the coordination surrounding of the Cu2+ ion by a tetrahedral one.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 798–802, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date. 相似文献
4.
Janusz Przes?awski Bogus?aw Kosturek Ryszard Jakubas 《Solid State Communications》2007,142(12):713-717
Thermal (specific heat) and optical (linear birefringence) studies were performed for a new ferroelectric crystal (C3N2H5)5Bi2Cl11. Two phase transitions were confirmed and described. The first-order paraelastic-ferroelastic phase transition at 360 K was studied with a polarizing microscope. The continuous second-order phase transition at 165 K to the ferroelectric phase is described by the Landau model using specific heat and linear birefringence data. The Landau expansion coefficients B and C are of an order of magnitude higher than the closely related ferroelectric crystal; MAPCB — (CH3NH3)5Bi2Cl11. Thermal parameters (such as the excess enthalpy and the excess entropy ) of the continuous transition were estimated and discussed. The ‘two-site’ model describing the motion of three of the five imidazolium cations, which is proposed from the structural studies, is fully confirmed by the data from the ac-calorimetric measurements. 相似文献
5.
Effects of lanthanum (La) substitution (0.003 ≤ x ≤ 0.015) on the dielectric and ferroelectric properties of Pb(Zr0.5Ti0.5)O3 thin films have been investigated. The films were synthesized on the Pt (1 1 1)/Ti/SiO2/Si (1 0 0) substrates by a sol-gel method. Large dielectric constants of the films are obtained within range of 800-1600 which are almost comparable to those observed in bulk ceramics. The films also show improved remnant polarization values and reduced coercive field values with the increasing addition of La substitution. Our results suggest that low La substitution contributes to enhance film electric properties due to the improvement of non-180° domain wall mobility as well as the stabilization of tetragonal phase. 相似文献
6.
M. Gargouri T. Mhiri M. Bouachir J. M. Rau J. Sngas A. Daoud 《Solid State Ionics》1997,100(3-4):225-232
The study by X-ray diffraction, calorimetry, vibrational and impedance spectroscopy of CsH(SO4)0.76(SeO4)0.24 new solid solution is presented. Crystals of this composition undergo two phase transitions at T = 333 and 408 K. The last one at 408 K is a superionic-protonic transition (SPT) related to a rapid [HS(Se)O4−] reorientation and fast H+ diffusion. A sudden jump in the conductivity plot confirms the presence of this transition. Above 408 K, this high temperature phase is characterized by high electrical conductivity (7 × 10t-3 Ω− cm−1) and low activation energy (Ea < 0.3 eV). 相似文献
7.
R. Geick O. Hofmann G. Wagner 《International Journal of Infrared and Millimeter Waves》1980,1(2):285-294
The dielectric constant of (CH3NH3)2 CdCl4 has been measured as a function of temperature in the submillimeter range. Freshly grown samples with a wide domain structure at room temperature show a pronounced dichroism in this spectral range which is caused by the orientation of the molecules in the room temperature orthorhombic phase and their response to the electromagnetic wave. 相似文献
8.
In the present study, various Pb[(Ni1/3Sb2/3)xTiyZrz]O3 where x+y+z=1, x=0.08 and y=0.44-0.49, ceramics in the morphotropic phase boundary (MPB) range were studied by dielectric and pyroelectric methods. The results of the investigations revealed an MPB composition range of y≅0.46. The study of the dielectric properties of these compounds as a function of temperature suggests that with increase in y the permittivity maximum increases and transition temperature shifts towards higher temperature. Well-saturated polarization versus electric field (P-E) hysteresis loops were obtained and values of Pr were calculated. The samples revealed good pyroelectric properties for y=0.44 and y=0.45 at room temperature with large figures of merit Fv=0.019 m2/C and FD=1.34×10-5Pa1/2. 相似文献
9.
Guangzu Zhang Shenglin Jiang Yangyang Zhang Tiantian Xie 《Current Applied Physics》2009,9(6):1434-1437
The bulk dense Pb[(Mn0.33Nb0.67)0.5(Mn0.33Sb0.67)0.5]0.08(ZrxTi1−x)0.92O3 pyroelectric ceramics have been successfully prepared by the conventional solid method. The effect of three phases coexistence in the ceramics is studied. When x = 0.95 and 0.85 in the ceramics, the maximum pyroelectric coefficient peaks appear at 23 °C and 45 °C, and the maximum values are 26.5 × 10−4 C/m2 °C and 25.5 × 10−4 C/m2 °C, respectively. The maximum pyroelectric coefficient appears large while the peaks widths are small. When the two kinds of ceramic powders mixed with the mol ratio of 2:1, the pyroelectric coefficient of the ceramics is above 10.0 × 10−4 C/m2 °C in a broad temperature range from 20 °C to 55 °C. The possible physical mechanism of the temperature broadened phenomenon is briefly discussed. 相似文献
10.
The chemical preparation, the calorimetric studies and the crystal structure are given for two new organic sulfates NH3(CH2)5NH3SO4 1.5H2O (DAP-S) and NH3(CH2)9NH3SO4·H2O (DAN-S). DAP-S is monoclinic P21/n with unit cell dimensions: a=11.9330(2) Å; b=10.9290(2) Å; c=17.5260(2) Å; β=101.873(1)°; V=2236.77(6) Å3; and Z=8. Its atomic arrangement is described as inorganic layers of units and water molecules separated by organic chains. DAN-S is monoclinic P21/c with unit cell parameters: a=5.768(2) Å; b=25.890(10) Å; c=11.177(5) Å; β=115.70(4)°; V=1504.0(11) Å3 and Z=4. Its structure exhibits infinite chains, parallel to the [100] direction where the organic cations are interconnected. In both structures a network of strong and weak hydrogen bonds connects the different components in the building of the crystal. 相似文献
11.
Xiaolian Chao Zupei Yang Xiaohui Huang Difei Ma Jinghui Zeng 《Current Applied Physics》2009,9(6):1283-1287
Effects of ZnO addition on electrical properties and low-temperature sintering of BiFeO3-modified Pb(Zr,Ti)O3–Pb(Fe2/3W1/3)O3–Pb(Mn1/3Nb2/3)O3 were investigated. The investigations revealed that the sintering temperature can be decreased to 950 °C, and the favorable properties were obtained with 0.10 wt% ZnO added ceramics. The electrical properties were as follows: d33 = 313 pC/N, Kp = 0.56, tan δ = 0.0053, εr = 1407 and Tc = 295 °C, which showed that this system was a promising material for the multilayer devices application. 相似文献
12.
Libing Chen Ruihong LiangHengchang Nie Zhiyong ZhouFei Cao Xianlin Dong 《Current Applied Physics》2014,14(11):1411-1415
Pure and Nb-doped Pb(Zr1−xTix)O3 (x = 0.47, 0.48, 0.50) ceramics were prepared by conventional solid-state reaction technique. Dielectric anomalies are observed in both kinds of samples near room temperature. The anomalies could be depressed by donor doping and prefer to be significant in ceramics with tetragonal crystallographic phase. Phase transition mechanism and domain wall pinning effect are proposed to explain this anomaly, and the former is considered as the dominated reason. Further results of the pyroelectric measurements confirm the existence of the ferroelectric–ferroelectric phase transition. 相似文献
13.
The microwave dielectric properties of La(Mg0.5−xCaxSn0.5)O3 ceramics were examined with a view to their exploitation for wireless communications. The La(Mg0.5−xCaxSn0.5)O3 ceramics were prepared by the conventional solid-state method with various sintering temperatures. The La(Mg0.5−xCaxSn0.5)O3 ceramics contained Ca2SnO4, CaSnO3, and La2O3. The amount of Ca2SnO4 increased with increasing sintering temperature. However, the relative amount of CaSnO3 decreased with increasing sintering temperature. An apparent density of 6.52 g/cm3, a dielectric constant (εr) of 20.2, a quality factor (Q×f) of 80,500 GHz, and a temperature coefficient of resonant frequency (τf) of −79 ppm/°C were obtained for La(Mg0.4Ca0.1Sn0.5)O3 ceramics that were sintered at 1500 °C for 4 h. 相似文献
14.
R.H. ChenS.C. Shern 《Journal of Physics and Chemistry of Solids》2002,63(11):2069-2077
Optical observation under the polarizing microscope and DSC measurements on K3H(SeO4)2 single crystal have been carried out in the temperature range 25-200 °C. It reveals a high-temperature structural phase transition at around 110 °C. The crystal system transformed from monoclinic to trigonal. Electrical impedance measurements of K3H(SeO4)2 were performed as a function of both temperature and frequency. The electrical conduction and dielectric relaxation have been studied. The temperature dependence of electrical conductivity indicates that the sample crystal became a fast ionic conductor in the high-temperature phase. The frequency dependence of conductivity follows the Jonscher's universal dynamic law with the relation σ(ω)=σ(0)+Aωn, where ω is the frequency of the AC field, and n is the exponent. The obtained n values decrease from 1.2 to 0.1 from the room temperature phase to fast ionic phase. The high ionic conductivity in the high-temperature phase is explained by the dynamical disordering of protons between the neighboring SeO4 groups, which provide more vacant sites in the crystal. 相似文献
15.
PbYb1/2Ta1/2O3 single crystals were obtained for the first time. They were grown by the flux method. The PbOPbF2B2O3 system was used as a solvent. Dielectric investigations were carried out in 1 0 0c, 1 1 0c and 1 1 1c pseudocubic directions. These studies pointed to anisotropy of dielectric properties. Frequency-independent ε′(T) and ε″(T) maxima related to the antiferroelectric–paraelectric (AFE—PE) phase transition are observed for all directions at 562 K. The frequency-dependent ε′(T) and ε″(T) maxima near 400 K related to the ferroelectric (FE)–AFE phase transition are observed only in 1 1 1c direction. The hysteresis loops were observed in this direction only. These results point that ferroelectric relaxor properties appear only in 1 1 1c direction. We propose to consider the ferroelectric phase as ferrielectric one. 相似文献
16.
Single crystal of a new [(CH3)2CHNH3]4Cd3Cl10 compound was grown and its properties have been characterized by dielectric and dilatometric investigations. Dielectric measurement evidenced the phase transitions at T1 = 352.8 K, T2 = 293.5 K and T3 = 261.5 K on cooling run. Dilatometric measurement of thermal expansion showed clearly two successive phase transitions at T1 and at T2. No temperature hysteresis was observed for phase transitions at T1 and T2. Large temperature hysteresis was observed at T3 in dielectric studies. Transitions at T1 and T3 are classified as a first order and at T2 as a continuous one. Anomalies of electric permittivity and expansion connected with the transitions are observed at practically the same temperatures and close to those observed earlier in DSC (Differential Scanning Calorimetry) studies. Results of dilatometric studies were applied to estimate critical coefficient β for continuous phase transition at T1 which is equal to 0.40 ± 0.01. 相似文献
17.
K. Strobel J. Frank K. Rosshirt R. Geick 《International Journal of Infrared and Millimeter Waves》1980,1(2):295-307
We have studied the
magnetic excitations of (CH3NH3)2MnCl4 in the antiferromagnetic and in the spin-flop regimes by means of magnetic resonance in the millimeter range (60–100 GHz). Rather odd line shapes of the resonance absorption line for narrow lines are explained as interference effects between the resonant and the non-resonant circular wave in the sample. For the antiferromagnetic resonance (AFMR) and for the paramagnetic resonance (EPR, above the Néel temperature), we have also studied the line width as a function of temperature. 相似文献
18.
The K absorption-edge spectra of the ligand chlorine ion in square-planar complex compounds cis- and trans-[Pt(NH3)2Cl2], trans-[Pd(NH3)2Cl2], and (NH4)2PdCl4 are reported and discussed in connection with the chlorine K absorption spectra of K2PtCl4 and K2PdCl4, reported previously. The observed chemical shift of a white line at the absorption threshold is interpreted in terms of the difference of the ligand-field splitting of electronic states for metal ions. The white line is attributed to the electronic transition from the Cl? ls level to the lowest unoccupied antibonding molecular orbital (MO), which is specified by a in the square-planar complex with D4h symmetry. The other absorption structures are regarded as continuum “shape resonances” of the outgoing electron trapped by the cage of the surrounding atoms. The effect of geometrical isomerism is found in the chlorine K absorption spectra of cis- and trans-[Pt(NH3)2Cl2]. 相似文献
19.
S. Wongsaenmai K. Kanchiang S. ChandarakY. Laosiritaworn S. RujirawatR. Yimnirun 《Current Applied Physics》2012,12(2):418-421
In this study, ceramics in Mn-doped ((Ka0.5Na0.5)0.935Li0.065)NbO3 ceramics (Mn content = 0.25, 0.50, 1.00 and 1.50 mol%) were successfully prepared by the conventional mixed-oxide technique. The crystal structure was identified by XRD as a single-phase perovskite structure with tetragonal symmetry. The valence of Mn ions, characterized by the synchrotron XAS technique, was seen to change from Mn4+ to Mn3+ during the formation of the crystal. The valence state of Mn strongly affected the crystal structure and ferroelectric properties of the ceramics. The ferroelectric parameters show the decrease of remnant polarization and the increase of the coercive field with increasing MnO2 content. The results confirm the Mn3+ in KNNL perovskite lattices, leading to the formation of oxygen vacancies and hardening effects. 相似文献
20.
J. Zaleski T. Glowiak R. Jakubas L. Sobczyk 《Journal of Physics and Chemistry of Solids》1989,50(12):1265-1269
A new [(C2H5)4N]6Bi8Cl30 crystal of the family of alkylammonium halogenobismuthates was grown. X-ray diffraction studies showed that the crystals are monoclinic, space group C2/m with a = 20.117(5), b = 12.682(3), c = 20.396(5) Å, β = 93.03(3), Z =2. The lattice consists of (C2H5)4N+ cations and a new type of Bi8Cl6−30 anion. Dielectric studies revealed two closely-lying structural phase transitions around 241 K (on cooling). They were interpreted as due to a freezing of the rotational motions of tetraethylammonium cations. 相似文献