Non-interferometric transient quantitative phase microscopy for ultrafast engineering

Lead-free piezoelectric ceramics Bi_0.5(Na_1-x-yK_xAg_y)_0.5TiO₃ [BNKAT(x/y)] have been synthesized by the mixed oxide method. The effects of the amount of K⁺ and Ag⁺ on the electrical properties were examined. X-ray diffraction patterns indicate that K⁺ and Ag⁺ ions partially substitute for the Na⁺ ions in Bi_0.5Na_0.5TiO₃ and form a solid solution during sintering. At room temperature, the ceramics exhibit good performances with piezoelectric constant d₃₃=189 pC/N, electromechanical coupling factor k_p=35.0%, remanent polarization P_r=39.5 μC/cm², and coercive field E_c=3.3 kV/mm, respectively. The curves of the dielectric constant ε_r and loss tangent tan δ versus temperature show that the transition temperature from ferroelectric to anti-ferroelectric phase decreases with increasing the K⁺ content for the compositions researched. The dependencies of k_p and polarization versus electric (P–E) hysteresis loops on temperature reveal that the depolarization temperature T_d of BNKAT(0.15/0.015) ceramics, which have good piezoelectric properties (d₃₃=134 pC/N, k_p=32.5%) and strong ferroelectricity (P_r=39.5 μC/cm², E_c=4.1 kV/mm) at room temperature, is above 160 °C. PACS 77.22.-d; 77.65.Bn; 77.80.Bh; 77.80.Dj; 77.84.Dy     

Polarization and piezoelectricity in polymer films with artificial void structure

Laminated polymer-film systems with well-defined void structures were prepared from fluoroethylenepropylene (FEP) and polytetrafluoroethylene (PTFE) layers. First the PTFE films were patterned and then fusion-bonded with the FEP films. The laminates were subjected to either corona or contact charging in order to obtain the desired piezoelectricity. The build-up of the “macro-dipoles” in the laminated films was studied by recording the electric hysteresis loops. The resulting electro-mechanical properties were investigated by means of dielectric resonance spectroscopy (DRS) and direct measurements of the stress-strain relationship. Moreover, the thermal stability of the piezoelectric d ₃₃ coefficient was investigated at elevated temperatures and via thermally stimulated discharge (TSD) current measurements in short circuit. For 150 μm thick laminated films, consisting of one 25 μm thick PTFE layer, two 12.5 μm thick FEP layers, and a void of 100 μm height, the critical voltage necessary for the build-up of the “macro-dipoles” in the inner voids was approximately 1400 V, which agrees with the value calculated from the Paschen Law. A quasi-static piezoelectric d ₃₃ coefficient up to 300 pC/N was observed after corona charging. The mechanical properties of the film systems are highly anisotropic. At room temperature, the Young’s moduli of the laminated film system are around 0.37 MPa in the thickness direction and 274 MPa in the lateral direction, respectively. Using these values, the theoretical shape anisotropy ratio of the void was calculated, which agrees well with experimental observation. Compared with films that do not exhibit structural regularity, the laminates showed improved thermal stability of the d ₃₃ coefficients. The thermal stability of d ₃₃ can be further improved by pre-aging. E.g., the reduction of the d ₃₃ value in the sample pre-aged at 150°C for 5 h was less than 5% after annealing for 30 h at a temperature of 90°C.     

Switching of banana liquid crystal mesophases under field

Taking advantage of the great number of bent-core or “banana" compounds synthesized and studied in the laboratory, we describe their behaviour under the application of an external electric field. If the field were a static one, we would work within the frame of an equilibrium phase diagram in a (field E, temperature T) space where some phases would be simple dielectrics and others ferroelectric ones with a macroscopic polarization, either spontaneous or induced by the field. In this paper, we deal with the basic responses of “banana” liquid crystals under the application of a low frequency (1 to 100 Hz) AC field. Firstly square-wave voltages allow us to locate the phase boundary between dielectric (at lower field) and ferroelectric phases (higher field) at a given temperature and field threshold. Then we apply slowly varying AC voltages with shapes like triangle or “triple-plateau” to check out the stability of the induced ferroelectric phase versus field removal. Three behaviours are encountered, the unstable one (short lifetime of the high-field ferroelectric phase) where the macroscopic polarization is destroyed and then rebuilt in the opposite direction during each half period and usually called “antiferroelectric”; the stable one (long lifetime) with a polarization that rotates at constant modulus which is labeled as “ferroelectric” and a new one where the macroscopic polarization is proportional to the applied fied, we named this behaviour as “superparaelectric”. Let us stress that these observations apply to the ferroelectric phases of the (E, T) phase diagram not to the zero field (0,T) phases observed in the usual phase characterization experiments except for an eventual spontaneous ferroelectric phase. Received 18 April 2002 and Received in final form 17 January 2003 Published online: 16 April 2003 RID="a" ID="a"e-mail: marcerou@crpp.u-bordeaux.fr RID="b" ID="b"URL: http://www.crpp-bordeaux.cnrs.fr     

Na0.5K0.5NbO3-BiFeO3 lead-free piezoelectric ceramics

Lead-free (Na_0.5K_0.5)NbO₃-based piezoelectric ceramics were successfully fabricated by substituting with a small amount of BiFeO₃ (BF). Difficulty in sintering of pure NKN ceramics can be eased by adding a few molar percent of BF, and the crystalline structure is also changed, leading to a morphotropic phase boundary (MPB) between ferroelectric orthorhombic and rhombohedral phases. The MPB exists near the 1-2 mol% BF-substituted NKN compositions, exhibiting enhanced ferroelectric, piezoelectric, and electromechanical properties of P_r=23.3 μC/cm², d₃₃=185 pC/N, and k_p=46%, compared to an ordinarily sintered pure NKN ceramics. The MPB composition has a Curie temperature of ∼370 °C, comparable to that of some commercial PZT materials.     

Structure, ferroelectric and piezoelectric properties of?(Bi0.98?xLa0.02Na1?x)0.5BaxTiO3 lead-free ceramics

Lead-free (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction show that La²⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi_0.5Na_0.5TiO₃ ceramics, the (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics possess much smaller coercive field E _c and larger remanent polarization P _r. Because of the low E _c (3.38 kV/mm), large P _r (46.2 μC/cm²) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d ₃₃=181 pC/N and k _p=36.3%. The depolarization temperature T _d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T _d.     

Electromechanical properties of lanthanum-doped lead hafnate titanate thin films for integrated piezoelectric MEMS applications

This paper focuses on the deposition and electromechanical characterization of lanthanum-doped lead hafnate titanate (PLHT) thin films as key material in piezoelectric microelectromechanical systems (pMEMS). PLHT (x/30/70) and PLHT(x/45/55) films with a thickness between 150 nm and 250 nm were deposited by chemical solution deposition (CSD). Thereby x varies between 0 and 10% La content. The electrical characterization shows that undoped (x=0) PLHT exhibit ferroelectric behavior similar to PZT of the same composition. La doping results in reduced ferroelectric properties and also affects the electromechanical properties. Measurements using a double beam laser interferometer yield a piezoelectric coefficient d ₃₃ of 60 pm/V, which stays constant with an increasing electric field. This leads to a linear displacement compared to undoped PLHT or conventional PZT films used for MEMS applications.     

Film structure and ferroelectric properties of in situ grown SrBi2Ta2O9 films

Ferroelectric SrBi₂Ta₂O₉ (SBT) films were grown by pulsed-laser deposition (PLD) at different substrate temperatures and fluences. A correlation between film structure and ferroelectric properties is established. The dielectric function ε^′ of thin SBT films shows a Curie–Weiss behavior well below the peak temperature T_max and relaxor-like behavior in the vicinity of T_max. Domain walls have a strong influence on the dielectric and ferroelectric properties and on the polarization fatigue of SBT films below 100 °C. The formation of ferroelectric phases is favored at lower substrate temperatures by incorporating Bi₂O₃ template layers into the structure. Received: 18 March 1999 / Accepted: 19 March 1999 / Published online: 5 May 1999     

Orientational contribution to the piezoelectric constants of BaTiO3 ceramic in ferroelectric phases with various symmetries

A self-consistent method based on the interaction of a piezoelectric sphere with a piezoelectric medium that has anisotropic elastic and dielectric properties is used to calculate the components of the tensor piezoelectric modulus of BaTiO₃ ceramic in all three ferroelectric modifications. A comparison of the calculated and measured piezoelectric moduli shows that at least 60–70% of the piezoelectric effect in BaTiO₃ ceramic is caused by domain boundary movement throughout the entire ferroelectric region. Fiz. Tverd. Tela (St. Petersburg) 41, 1080–1083 (June 1999)     

Piezoelectric measurements on BiFeO3 single crystal by Raman scattering

The piezoelectric response of BiFeO₃ at low temperature has been investigated by Raman scattering measurements. The application of an external electric field at T=10 K induces frequency shifts of the lowest frequency mode related to the Bi-O bonds and corresponding to the soft mode of the ferroelectric transition. The piezoelectric effect is responsible for the softening of this mode via the tensile stress leading to the expansion of the crystal. The phonon deformation potential associated with the soft mode has been estimated around −200 cm⁻¹/strain units using the linear piezoelectric coefficient d₃₃=16 pm/V. It found in the range of the ones obtained for typical piezoelectrics.     

Heat conductivity and the Lorentz number of the Sm1−x GdxS “black” phase

Measurement of the heat conductivity and electrical resistivity of two Sm_1−x Gd_xS compositions with x=0.1 and 0.14 is reported within the 80–300 K interval. An analysis of experimental data on the electronic component of heat conductivity permits a conclusion that the d subband of “heavy” carriers in the conduction band of these materials lies above the s “light”-carrier subband. Fiz. Tverd. Tela (St. Petersburg) 41, 26–29 (January 1999)     

Dielectric, ferroelectric and piezoelectric properties of 0-3 barium titanate–Portland cement composites

In this work, barium titanate (BT) and cement composites of 0-3 connectivity were produced with BT concentrations of 30%, 50% and 70% by volume using the mixing and pressing method. The dielectric constant (ε _r ) and the dielectric loss (tan δ) at room temperature and at various frequencies (0.1–20 kHz) of the ferroelectric BT-Portland cement composites with different BT concentrations were investigated. The results show that the dielectric constant of BT-PC composites was found to increase as BT concentration increases, and that the highest value for ε _r —of 436—was obtained for a BT concentration of 70%. In addition, the dielectric loss tangent decreased with increasing BT concentration. Moreover, several mathematical models were used; the experimental values of the dielectric constants are closest to those calculated from the cube model. The 0-3 cement-based piezoelectric composites show typical ferroelectric hysteresis loops at room temperature. The instantaneous remnant polarization (P _ir ), at an applied external electrical field (E ₀) of 20 kV/cm (90 Hz) of 70% barium titanate composite, was found to have a value ≈3.42 μC/cm². Furthermore, the piezoelectric coefficient (d ₃₃) was also found to increase as BT concentration increases, as expected. The highest value for d ₃₃ was 16 pC/N for 70% BT composite.     

Simultaneous measurement of the piezoelectric and dielectric response of nanoscale ferroelectric capacitors by an atomic force microscopy based approach

We present a sensitive method to simultaneously acquire the C(V ) characteristics and piezoresponse of sub-micron size ferroelectric capacitors using an Atomic Force Microscope (AFM). Model Pt/(La_0.5,Sr_0.5)CoO₃/PbZr_0.4Ti_0.6 O₃/(La_0.5,Sr_0.5)CoO₃/La:SrTiO₃/Si nanocapacitors were fabricated by focused ion beam milling from 100 μm² down to 0.04 μm². With this AFM based capacitance measurement technique we show clear “double-humped” C(V ) for all sizes with no significant change in the peak value of the ε_r down to capacitors with the smallest area of 0.04 μm². The smallest capacitance measured is only of the order a few femtofarads, demonstrating the high sensitivity of the technique. Simultaneously, the piezoelectric response is recorded for each measurement, thus the technique facilitates simultaneous piezoresponse and dielectric characterization of ferroelectric memory devices. PACS 77.55.+f; 77.90.+k; 85.50.-n; 77.84.-s     

有序结构氟聚合物压电驻极体的制备和压电性研究

描述了一种有序微孔结构压电聚合物功能膜的制备方法,利用模板的高度有序实现薄膜微孔结构的精确控制.将此制备方法用于氟聚合物压电驻极体薄膜的制备,通过扫描电子显微镜(SEM)对其微观结构的观察表明薄膜具有理想的有序结构.对氟聚合物压电驻极体压电性的研究则是利用正压电效应测量准静态压电系数d₃₃,通过等温衰减和压强依赖性的测量考察其压电性能.结果表明:有序结构氟聚合物压电驻极体的准静态压电系数d₃₃可高达300 pC/N;与无序结构氟聚合物     

Bipolar cycling effects in BiFeO3–BaTiO3 piezoelectric ceramics

BiFeO₃–BaTiO₃ (BF-BT) lead-free piezoelectric system has been paid much attention due to good piezoelectric properties and high Curie temperature. Poling is a process to align ferroelectric domains and increase the piezoelectric coefficients. During the poling process, unipolar direct current (dc) electric fields were applied conventionally, but recently bipolar alternating current (ac) cycling was reported to improve piezoelectric properties in rhombohedral structure piezoelectric materials. We investigated the effects of dc-poling and ac-cycling in BF-BT ceramics. The d₃₃ increased from 210 pC/N with dc-poling to 240 pC/N with ac-cycling in the morphotropic phase boundary region of BF-BT with domain engineering. This improvement of piezoelectric properties with ac-cycling was consistent with the structural evolution related to ferroelectric domains.     

Properties of Sr- and Sb-doped PZT–Portland cement composites

Lead zirconate titanate (PZT) ceramic-cement-based composites have increasingly been recognized as an attractive new composite material for use as a sensor in structural applications. In this work, PZT was doped with Sr and Sb (PSZT) to give it greater dielectric constant (ε _r) and higher piezoelectric coefficient (d ₃₃) values than normal PZT and is the first time that it is mixed with normal Portland cement to produce a 0–3 connectivity PSZT–Portland cement composite using PSZT contents of 50% and 70% by volume. Scanning electron micrographs show PSZT ceramic particles closely surrounded by the hydrated cement matrix where a dense microstructure can be observed in the interfacial zone. Both the ε _r and d ₃₃ values were found to increase with PSZT content and the values are amongst the highest so far for these types of composites, where the ε _r and d ₃₃ values reached 590 and 48 pC/N, respectively.     

Experimental study of the energy gap in the spin-wave spectrum in Co/Pd multilayer films

The energy gap appearing in the spin-wave spectrum as a result of Bragg scattering by the modulation period q=2π/(d ₁+d ₂) of a one-dimensional superlattice is observed by the method of spin-wave resonance in Co/Pd multilayer films. It is shown that this gap is asymmetric: The “positive” deviation is from two to three times greater than the “negative” deviation. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 12, 938–941 (25 June 1996)     

Dielectric,ferroelectric and field-induced strain response of lead-free BaZrO3-modified Bi0.5Na0.5TiO3 ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xBaZrO₃ (BNT–BZ100x, with x = 0–0.10) were prepared using a conventional solid-state reaction method. The crystal structure, microstructure, dielectric, ferroelectric, and piezoelectric properties of BNT–BZ100x ceramics were studied as functions of different BZ content. X-ray diffraction patterns revealed that the BZ completely diffused in the BNT lattice in the studied composition range. An appropriate amount of BZ addition improved the dielectric, ferroelectric, and piezoelectric properties of BNT ceramics. The remanent polarization (P_r) and piezoelectric constant (d₃₃) increased from 22 μC/cm² and 60 pC/N for pure BNT to 30 μC/cm² and 112 pC/N for x = 0.040, respectively. In addition, electric field-induced strain was enhanced to its maximum value (S_max = 0.40%) with normalized strain (d*₃₃ = S_max/E_max = 500 pm/V) at an applied electric field of 8 kV/mm for x = 0.055. The enhanced strain can be attributed to the coexistence of ferroelectric and relaxor ferroelectric phases.     

Viscosity at small scales in polymer melts

Flows around small colloidal particles of diameter b, or in thin films, capillaries, etc., cannot always be described in terms of the macroscopic polymer viscosity. We discuss these features for entangled polymer melts, where two distinct regimes can be found: (a) the thin regime where b is smaller than the coil radius R₀, but larger than the diameter of the Edwards tube; (b) the ultrathin regime, where . We consider (i) non adsorbing particles, where slippage may occur between the melt and the solid surface; (ii) “hairy” particles, which carry some bound polymer chains. We obtain scaling predictions for mobilities of spheres, of needles, and of clusters of particles. We also discuss translational and rotational diffusion of needles. Received 19 April 1999     

Griffiths phase manifestation in disordered dielectrics

We predict the existence of a Griffiths phase in dielectrics with a concentrational crossover between dipole glass (electric analog of spin glass) and ferroelectricity. Particular representatives of the above substances are KTaO₃:Li, Nb, Na, or relaxor ferroelectrics like Pb_1–xLa_xZr_0.65Ti_0.35O₃. Since this phase exists above the ferroelectric phase-transition temperature (but below that temperature for ordered substances), we call it a “para-glass phase”. We assert that the difference between paraelectric and para-glass phases in the above substances is the existence of clusters (inherent to the “ordinary” Griffiths phase of Ising magnets) of correlated dipoles. We show that randomness plays a decisive role in the Griffiths (para-glass) phase formation: this phase does not exist in a mean field approximation. To investigate the Griffiths phase properties, we calculate the density of Yang-Lee (YL) zeros in the partition function and find that it has “tails” inherent to the Griffiths phase in the above temperature interval. We perform calculations on the basis of our self-consistent equation for the long-range order parameter in an external electric field. This equation has been derived in the framework of the random field theory. The latter automatically incorporates both short-range (due to indirect interaction via transverse optical phonons of the host lattice) and long-range (ordinary dipole-dipole) interactions between impurity dipoles, so that the problem of long-range interaction considerations does not appear in it. Received 17 May 2000