Piezoelectric relaxations in homopolymers and copolymers of γ-Benzyl-L-glutamate and L-Leueine

The temperature dependence of the piezoelectric stress-constant, the piezoelectric strain-constant, and the Young's elastic constant is simultaneously determined for homopolymers and copolymers of γ-benzyl-L-glutamate [Glu(OBz)] and L-leucine (Leu). With the rise of temperature, the piezoelectric constants first increase due to the elastic relaxation in the Leu side chains (about ?150°C) and the Glu(OBz) side chains (about ?10°C), and then decrease due to the dielectric relaxation in the Glu(OBz) side chains. Higher piezoelectric constants are observed for the copolymers at low temperatures. This suggests that the shear-induced internal strain of the peptide dipoles is enhanced by heterogenity in the structure of side chains.     

Piezoelectric activity and phase transitions in (PMN)0.69(PT)0.31 single crystal

Piezoelectric and dielectric investigations have been performed on a (PMN)_0.69(PT)_0.31 single crystal. Low frequency (100?Hz) dielectric permittivity measurements revealed distinct anomaly at 129°C (T _εmax) corresponding to the structural transformation from the tetragonal to cubic phase. Two other anomalies have been detected at 90 and 96°C. After preliminary polarization in the d.c. electric field, switched on above T _εmax and switched off inside the tetragonal phase, the piezoelectric activity has been observed in function of temperature. Values of the piezoelectric resonance frequencies changed markedly at 96°C (on cooling) and 124°C (on heating) showing clear softening of the elastic properties near these temperatures. Values of the piezoelectric and electromechanical coupling coefficients obtained were respectively of the order of 800?pCN^?1 (d ₃₁) and 0.35?(k ₃₁). Piezoelectric activity was detected tens of degrees above the temperature T _εmax and disappeared at temperature at which the dispersion of the dielectric permittivity due to the presence of polar nanoregions is negligible. It was found that strong softening of the elastic properties accompanies phase transitions to the tetragonal and monoclinic phase.     

Dielectric and acoustic properties of the new lead-free BiLi<Subscript>0.6</Subscript>W<Subscript>0.4</Subscript>O<Subscript>3</Subscript> ceramic

The properties of the new lead-free compound BiLi_0.6W_0.4O₃, obtained using ceramic technology, were studied by dielectric and mechanical spectroscopy. The anomalies of internal friction are, along with the elastic and dielectric properties observed experimentally at a temperature of 350°C, related to its structural phase transition. Dielectric and mechanical relaxation due to processes of interaction between crystal lattice defects was revealed in the low-temperature phase.     

On the low temperature phase transition in (NH4)2SO4

An ultracryostat and multidecameter were used to determine the temperature dependence of the dielectric constant ?′ and dielectric loss ?″ over a wide range of frequencies of single crystals and polycrystalline samples of (NH₄)₂SO₄ in the region of the low temperature phase transition. A sharp increase was observed in the values of ?′ and ?″ at about ?50°C. In addition, a dielectric dispersion was detected and found to be more pronounced in the high temperature phase. This dispersion was attributed to piezoelectric resonance. The observed sudden increase in the values of the dielectric constant and dielectric loss below ? 50°C was attributed to the ferroelectric nature of the low temperature phase of (NH₄)₂SO₄.A DTA thermogram showed a sharp peak at ? 50°C which indicated that the phase transition is one of first order type. A TMA thermogram showed that this transformation was associated with a rapid increase in the expansion coefficient. Such an increase in the lattice parameter might be attributed to the enhanced rotation of electric dipoles associated with the distorted NH₄⁺ and SO₄^2? ions. The distortion of both the ammonium and sulfate ions in addition to their expected orientational motion are suggested to be responsible for the ferroelectric behaviour of ammonium sulfate below ?50°C.A transition to a metastable hexagonal state at about ?40°C is thought to occur, and this transformation is found to be irreversible.     

Ca3NbGa3Si2O14晶体的介电和压电特性

利用Y切和(yxl)30°切两种样品测量了Ca3NbGa3Si2O14晶体的介电、压 电和部分弹性参数.计算了(yxl)θ切型相关压电常数随切角的变化.与La3Ga5SiO14晶体相比，Ca3NbGa3Si2O14晶体具有更优良的压电性能，其压电常数 d11=7.93×10-12C/N，d14=-5.88×10-12C/N. 关键词： Ca3NbGa3Si2O14晶体 介电常数 压电常数     

Piezĭlectric and elastic properties of Sr<Subscript>3</Subscript>NbGa<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>14</Subscript> (SNGS) single crystals

The elastic, piezoelectric, and dielectric constants of new piezoelectric single crystals Sr₃NbGa₃Si₂O₁₄ (SNGS) are measured. The elastic moduli C ₁₁ and C ₆₆ and the piezoelectric coefficient e ₁₁ are determined over a wide temperature range. It is demonstrated that the piezoelectric activity of the crystal is retained up to the highest temperatures (900°C).     

Dielectric loss as an indication of the kinetics of the ferroelectric phase transition

The dependences tanδ(f, T) for triglycine sulfate and diglycine nitrate single crystals are investigated in the frequency range f = 1?2 × 10⁷ Hz at temperatures from ?150 to 50°C for triglycine sulfate and from ?150 to ?60°C for diglycine nitrate. The results are discussed in the framework of the model according to which two or more types of media with different dielectric properties are formed in the ferroelectric phase. The polar volumes of domains themselves and the volumes of domain walls with different symmetries are treated as individual media. The dependences tanδ(f, T) make it possible to separate the contribution of a particular medium and to trace its evolution with temperature. The results of the analysis of the relaxation properties confirm that the phase transitions lead to the formation of two media (the polar medium and domain walls) in triglycine sulfate and three media (the polar medium and two types of domain walls) in diglycine nitrate. It is demonstrated that the relaxation properties are not steady-state characteristics of the samples but depend on their prehistory.     

High-temperature electromechanical properties of strontium-doped langasite

Langasite (La₃Ga₅SiO₁₄) is a suitable piezoelectric material for high-temperature bulk acoustic wave applications such as resonant microbalances and gas sensors using specific surface affinity layers. Langasite has been shown to exhibit bulk oscillations at temperatures of up to 1400 °C. Factors limiting its use as piezoelectric transducer at elevated temperatures such as excessive conductive and viscous damping are presented and discussed.The paper focuses on the investigation of the defect chemistry and transport mechanisms in strontium-doped langasite single crystals. It is found that strontium suppresses point defect relaxations observed in langasite up to about 400 °C. Thereby viscous damping could be lowered up to this temperature. Between about 400 and 600 °C strontium-doping does not impact the damping. Further, strontium dopants enhance the movement of oxygen ions via creation of oxygen vacancies above about 600 °C leading to a slight increase in damping. One concludes, that the relatively strong impact on damping exhibited by ionic defects can be utilized by the application of acceptor doping at elevated temperatures.     

Characterization of lead free (K0.5Na0.5)NbO3-LiSbO3 piezoceramic

(K_0.5Na_0.5)NbO₃ (KNN) based lead free ceramics have been fabricated by a solid state reaction. In this work, LiSbO₃ (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained. The detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method. The full set of material constants for the obtained polycrystalline ceramics were determined and compared to the pure hot pressed KNN counterpart. KNN-LS polycrystalline ceramic was found to have higher elastic compliance, dielectric permittivity and piezoelectric strain coefficients, but lower mechanical quality factor, when compared to pure KNN, exhibiting a “softening” behavior. However, a high coercive field (∼17 kV/cm) was found for the LS modified KNN material. The properties as a function of temperature were determined in the range of −50-250 ^°C, showing a polymorphic phase transition near room temperature, giving rise to improved piezoelectric behavior.     

铁电晶体(K0.20Na0.20Sr0.60Ba0.20)Nb2O6全部电弹常数的测定

本文讨论了由作者首次人工合成的新的钨青铜结构铁电单晶(K_0.20Na_0.20Sr_0.60Ba_0.20)Nb₂O₆全部电弹常数的测量方法和测量程序。第一次发表了该晶体的全部电弹常数及电-机耦合系数等共53个数据。绝大多数的数据是按IRE标准进行测量的。采用了(zxl)45°切片的厚度切变振动模式和(xzt)45°棒的长度扩张模式来测定弹性系数s₆₆^D和s₁₃^D。对实验过程引起的测量误差进行了讨论。 关键词：     

Relaxation dynamics of poly(vinylidene fluoride) studied by dynamical mechanical measurements and dielectric spectroscopy

The aim of this study is to analyze the mobility of polymer chains in semicrystalline poly(vinylidene fluoride) (PVDF). PVDF crystallizes from the melt in the α crystalline phase. The transformation from the α phase to the electroactive β phase can be induced by stretching at temperatures in the range between 80 and 140 °C. The spherulitic structure of the crystalline phase is deformed during stretching to form fibrils oriented in the direction of the strain. The amorphous phase confined among the crystalline lamellae is distorted as well and some degree of orientation of the polymer chains is expected. Dynamic-mechanical and dielectric spectroscopy measurements were performed in PVDF films stretched to strain ratios up to 5 at temperatures between 80 and 140 °C. Dynamic-mechanical measurements were conducted between -60 °C and melting and in this temperature range the relaxation spectra show the main relaxation of the amorphous phase (called β-relaxation) and at higher temperatures a relaxation related to crystallites motions (α (c)-relaxation). Although the mean relaxation times of the β-relaxation are nearly equal in PVDF before and after crystal phase transformation, a significant change of shape of the relaxation spectrum proves the effect of chain distortion due to crystal reorganization. In stretched PVDF the elastic modulus of the polymer in the direction of deformation is significantly higher than in the transversal one, as expected by chain and crystals fibril orientation. The recovery of the deformation when the sample is heated is related with the appearance of the α (c)-relaxation. Dielectric spectroscopy spectrum shows the main relaxation of the amorphous phase and a secondary process (γ-relaxation) at lower temperatures. Stretching produces significant changes in the relaxation processes, mainly in the strength and shape of the main relaxation β. The Havriliak-Negami function has been applied to analyze the dielectric response.     

Studies of dielectric relaxation in natural fiber–polymer composites

Polymer composites of a polyester resin matrix filled with short palm tree lignocellulosic fibers were studies by means of dielectric spectroscopy in the frequency range 0, 1–100 kHz and temperature interval from 40 °C to 200 °C. Three relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in Palm fiber, the relaxation process associated with conductivity occurring as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and the interfacial relaxation that is attributable to the accumulation of charges at the Palm fibers/polyester interfaces.     

Acoustic anomalies and relaxation dynamics of relaxor ferroelectric Na1/2Bi1/2TiO3 single crystals studied by using Brillouin spectroscopy

Acoustic anomalies of relaxor ferroelectric Na_1/2Bi_1/2TiO₃ single crystals were investigated over a wide temperature range from −196 °C to 900 °C by using Brillouin spectroscopy. The longitudinal sound velocity, the acoustic absorption coefficient and the elastic constant C₁₁ were determined for the acoustic phonon mode propagating in the [100] direction. Two acoustic anomalies, weaker ones at the cubic-tetragonal phase transition temperature of ~540 °C and more pronounced ones at temperatures near 315 °C near the dielectric maximum temperature, were investigated and discussed in relation with the relevant order parameters coupled to the acoustic waves. The relaxation dynamics in the cubic phase were studied based on the flattening of the mode frequency and the half width, which was observed for the first time, and a modified Arrhenius law.     

Dielectric relaxation studies of four aliphatic esters in benzene at 30°, 40°, 50° and 60°

The complex permittivity at 9.92 GHz, the static permittivity and the high frequency limiting permittivity have been determined for n-butyl-acrylate, allyl-methacrylate, isobutyl-methacrylate and isobutyl-acrylate monomers in benzene at 30°, 40°, 50° and 60°C. The relaxation time values and the dipole moment values calculated from these data employing different methods, are interpreted in terms of the molecular and the intramolecular rotations. Various thermodynamic parameters calculated for the dielectric relaxation as well as the viscous flow processes also suggest the existence of both the intramolecular and the overall orientations in these monomer esters. The comparative study of enthalpies of activation for the dipolar relaxation and the viscous flow suggests the absence of any solid rotator phase in these molecules. Values of the Debye's factor and the Kalman's factor show that the Kalman's equation represents the relation between the dielectric relaxation and the viscosity, more satisfactorily than the Debye's equation.     

Orientation dependence of electrical properties of 0.96Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-0.04BaTiO<Subscript>3</Subscript> lead-free piezoelectric single crystal

In this paper, a single crystal of 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ with dimensions of Φ 30×10 mm was grown by the top-seeded-solution growth method. X-ray powder diffraction results show that the as-grown crystal possesses the rhombohedral perovskite-type structure. The dielectric, piezoelectric and electrical conductivity properties were systematically investigated with 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples. The room-temperature dielectric constants for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples are found to be 650, 740 and 400 at 1 kHz. The (T _m, ε _m) values of the dielectric temperature spectra are almost independent of the crystal orientations; they are (306°C, 3718), (305°C, 3613) and (307°C, 3600) at 1 kHz for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal. The optimum poling conditions were obtained by investigating the piezoelectric constants d ₃₃ as a function of poling temperature and poling electric field. For the 〈001〉 and 〈110〉 crystal samples, the maximum d ₃₃ values of 146 and 117 pC/N are obtained when a poling electric field of 3.5 kV/mm and a poling temperature of 80°C were applied during the poling process. The as-grown 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ crystal possesses a relatively large dc electrical conductivity, especially at higher temperature, having a value of 1.98×10⁻¹¹ Ω⁻¹⋅m⁻¹ and 3.95×10⁻⁹ Ω⁻¹⋅m⁻¹ at 25°C and 150°C for the 〈001〉 oriented crystal sample.     

Inelastic light scattering studies of diffuse phase transition in ferroelectric Sr1.9Ca0.1NaNb5O15 thin films

The dynamic behavior of highly oriented ferroelectric Sr_1.9Ca_0.1NaNb₅O₁₅ thin films has been investigated by Brillouin light scattering over a wide temperature range between 25 and 450 °C. The temperature variations of the full‐width at half‐maximum (FWHM) of the central peak (CP) are found to exhibit marked changes around the Curie temperature (T_c = 246 °C). The CP reveals a relaxational mode behavior, which is attributed to thermally activated fast relaxation of polar nanoregions (PNRs). The width of the CP decreases steadily upon cooling from ∼400 °C to T_c and shows little subsequent change within the ferroelectric state, indicating an increase of the number of PNRs and a slowing down of their dynamics. By using a modified superparaelectric model, the activation energy (H₀) of the relaxation processes and the Burns temperature (T_B) are determined to be 2939 and 385 °C, respectively. The evidence for this diffuse phase transition provided by Brillouin scattering is in agreement with results obtained from the temperature‐dependent dielectric permittivity, refractive index, and Raman spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Structural phase transition in ferroelectric NH4103

The structural phase transformation between the ferroelectric and paraelectric form of NH₄IO, near 83°C is dominated by tilt motions of IO₆-octahedra within a perovskite-like framework. Simultaneously, small displacements of NH₄ along the polar axis give rise to a switchable spontaneous polarization at low temperatures. As the transition mechanism is governed by the tilting of octahedra and not by the appearance of ferroelectricity, NH₄IO₃ is characterised as an improper ferroelectric material. Although the space group of the high-temperature β-phase is polar, the polarization moment is zero. Raman-active thermal soft modes appear in the ferroelectric phase. The phase transition is first order with anomalies of dielectric, piezoelectric and elastic constants.     

Mechanical properties of the alloy 36NKhTYu in relation to the mechanisms underlying the precipitation of the γ′ and η phases. III

The kinetic characteristics of the changes in elastic limit, ductility, and stress relaxation taking place in samples of the alloy 36NKhTYu on aging at 700°C are considered in relation to aging time, the measurements being made at 20 and 600°C. The samples are initially taken in five different states induced by various forms of preliminary treatment, being distinguished from one another with respect to grain size, mechanism of γ phase precipitation, and state of the grain boundaries. In order to obtain material with a high elastic limit, working at moderately low temperatures, the discontinuous precipitation of the strengthening phase has certain clear advantages over continuous precipitation. For high working temperatures, in which grain-boundary stress relaxation starts playing an appreciable role, however, it is undesirable that discontinuous decomposition should undergo any major development in the aging of the material.     

Low-temperature relaxations in amorphous polyolefins

The dynamic mechanical relaxation behavior (1cps) of two series of amorphous polyolefins, ─(CH₂)_mC(CH₃)₂─ and ─(CH₂)_mC(CH₃)(CH₂ CH₃)─ where m = 1, 2, 3 was investigated from 4.2°K to the glass transition. Most of the polymers show a damping maximum or pleateau in the 40 to 50°K region. Various mechanisms which have been suggested for cryogenic relaxations in amorphous polymers are considered as they might relate to the polyolefins. Two secondary relaxation processes above 80°K are distinguished. A relaxation at about 160°K (β) in the second and third member of each series is associated with restricted backbone motion. This process requires a certain degree of chain flexibility since it is not observed in the first member of each series. A lower Temperature process (γ) is observed in each member of the second series and is attributed to motion of the ethyl side group.     

Structural and electrical properties of 0.7Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>–0.3PbTiO<Subscript>3</Subscript> thin films grown on Ir/MgO buffered Si(100) substrates

Thin films of 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN-PT) have been grown on Ir/MgO buffered Si(100) substrates at different substrate temperatures by pulsed laser deposition. Crystalline phases as well as preferred orientations in the PMN-PT films were investigated by X-ray diffraction analysis (XRD). The microstructure, dielectric and ferroelectric properties of PMN-PT film prepared at 650 °C were studied. The results show that the film prepared at 650 °C exhibits pure perovskite phase and single c-axis orientation. The dielectric constant and dissipation factor of the single c-axis oriented film are 1000 and 0.04 at a frequency of 1 kHz, while the remnant polarization and coercive field are about 13.0 μC/cm² and 100 kV/cm under an electric field of 480 kV/cm, respectively. PACS 81.15.Fg; 77.80.-e; 77. 22.Ej; 77.55.+f; 85.50.Gk