Dielectric and pyroelectric properties of a composite of ferroelectric ceramic and polyurethane

Flexible piezo- and pyroelectric composite was made in the thin film form by spin coating. Lead Zirconate Titanate (PZT) ceramic powder was dispersed in a castor oil-based polyurethane (PU) matrix, providing a composite with 0–3 connectivity. The dielectric data, measured over a wide range of frequency (10^–5 Hz to 10⁵ Hz), shows a loss peak around 100 Hz related with impurities in the polymer matrix. There is also an evidence of a peak in the range 10^–4 Hz, possibly originating from the glass transition temperature T_g of the polymer. The pyroelectric coefficient at 343 K is 7.0×10^–5 C·m^–2·K^–1 which is higher than that of β-PVDF (1×10^–5 C·m^–2·K^–1). Electronic Publication     

YBaCuO ceramics-based DC interferometer with current-formed weak links

The results of the study of dc interferometers and SQUIDS from the thick-film YBa_1·5Ca_0·5Cu₃O_7\t-\gd ceramics are presented here. It is shown that under the influence of high-density currents through the film constriction the differential resistance of interferometers thus formed increases by 2–3 orders of magnitude and the voltage-field characteristics become more regular. The frequency dependence of intrinsic noise in dc SQUIDs based on thick-film interferometers is investigated. It is demonstrated that in the white noise frequency region (1–10 Hz) the energy sensitivity is withinδɛ _n =10⁻²⁸ to 10⁻²⁹ J/Hz.     

Study of dielectric properties of RbNO3 single crystals

Dielectric properties, dielectric constant (k), dielectric loss (tan δ) and a.c. conductivity (σ) in the solution-grown single crystals of RbNO₃ are presented from room temperature to about 200°C covering the frequency range 10² to 10⁵ Hz. A broad peak observed in tan δ-frequency data between 10³ and 10⁵Hz is thought to be due to impurity-vacancy dipoles. The sudden rise of three parameters near 160°C is attributed to the known phase transition from trigonal to CsCl structure.     

Polymer-metal chelate precursor reduced its firing temperature and time for preparing yttrium barium cuprate powder

Bulk YBa₂Cu₃O _x was prepared by a polymer chelate precursor method using poly[(N,Ndicarboxymethyl)allylamine] as a chelating polymer of which molecular weights were 3 × 10⁴ (PDAA-L) and 3 × 10⁵ (PDAA-H), respectively. X-ray diffraction (XRD) analysis of the precursor from PDAA-H shows that YBa₂Cu₃O _x (Y123) phase appeared after being calcined at 750 °C for 5 h and the mixture was completely converted to tetragonal Y123 phase after being calcined at 800 °C for 5 h. The phase evolution of the precursor from PDAA-H during isothermal experiment at 800 °C showed that pure tetragonal Y123 was produced even after the polymer chelate precursor was heated for 2 h in air, although a very small amount of BaCO₃ was recognized. This BaCO₃ phase was hardly recognized after 4 h calcination. The precursor prepared from PDAA-L was fully converted to pure tetragonal Y123 after 3 h calcining at 800 °C. On the other hand, the sample prepared from metal nitrate solution without PDAA was not fully transferred to Y123 phase after heating at 800 °C for 10 h. Large amounts of Y₂O₃, BaCO₃ and CuO were observed. These results indicated that the greater homogeneity in the polymer chelate precursor leads to reduced firing times and temperature compared with the metal nitrate precursor.     

Influence of Zr doping on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

Pure and Zr-substituted CaCu₃(Ti_1−x Zr _x )₄O₁₂ (x = 0, 0.01, 0.02, 0.03) ceramics were prepared by the Pechini method. X-ray powder diffraction analysis indicated the formation of single-phase compound, and all the diffraction peaks were completely indexed by the body-centered cubic perovskite-related structure. The effects of Zr⁴⁺ ion substituting partially Ti⁴⁺ ion on the dielectric properties were investigated in frequency range between 100 Hz and 1 GHz. The low frequency (f ≤ 10⁵ Hz) dielectric constant decreases with Zr substitution and the high frequency (f ≥ 10⁷ Hz) dielectric constant is unchanged. Interestingly, a low-frequency relaxation was observed at room temperature through Zr substitution. The observed dielectric properties in Zr-substituted samples were discussed using the internal barrier layer capacitor model. A corresponding equivalent circuit was adopted to explain the dielectric dispersion. The characteristic frequency of low-frequency relaxation rises due to the decrease of the resistivity of grain boundary with Zr substitution, which is likely responsible for the large low-frequency response at room temperature.     

Frequency-dependent dielectric properties and electrical conductivity of CdIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

The real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity and ac conductivity (σ_ac) of CdIn₂S₄ single crystals (cubic structure) have been measured in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. In the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz, the ac conductivity of single-crystal CdIn₂S₄ follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level.     

Synthesis and nonlinear optical properties of novel Y-type polyurethanes with high thermal stability of dipole alignment

2,3-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3′-dimethoxy-4,4′-biphenylenediisocyanate to yield novel Y-type polyurethanes 4–5 containing 2,3-dioxy benzylidenemalononitrile group as a nonlinear optical (NLO)-chromophore, which constituted parts of the polymer backbones. Polyurethanes 4–5 were soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed a thermal stability up to 270 °C in thermogravimetric analysis thermograms and the glass-transition temperatures (T _g) obtained from differential scanning calorimetry thermograms were around 116–135 °C. The second harmonic generation (SHG) coefficients (d ₃₃) of poled polymer films at 106.4 mm⁻¹ fundamental wavelength were around 9.07 × 10⁻¹⁹ C (2.72 × 10⁻⁹ esu). The dipole alignment exhibited high thermal stability up to 10 °C higher than T _g, and there was no SHG decay below 145 °C due to the partial main-chain character of the polymer structure, which was acceptable for nonlinear optical device applications.     

Electronic Conduction in the Na2O ·nAl2O3–Y2O3 System

The electronic conductivity of Na₂O · nAl₂O₃–Y₂O₃ materials is found to vary from 10^–5 to 10^–1 S/m between room temperature and 800°C and to increase from 10^–5 to 10^–4 S/m as the frequency increases from 100 Hz to 200 kHz. The temperature variation of conductivity is interpreted in terms of the energy band structure.     

Electrochemical synthesis and characterization of a new soluble conducting polymer

Electroactive poly(4-methyl carbazole-3-carboxylic acid) (PMCCA) film was formed on Pt electrode surface by oxidative electropolymerization of a new carbazole derivative. The structure of the soluble polymer was elucidated by nuclear magnetic resonance (¹H and ¹³C NMR) and Fourier transform infrared (FTIR) spectroscopy. The average molecular weight has been determined by gel permeation chromatography (GPC) to be M _n = 51,000 for the electrochemically synthesized polymer. Characterizations of the resulting polymer were performed by cyclic voltammetry, dry conductivity measurement, scanning electron microscopy, and UV-vis spectroscopy. Spectroelectrochemical studies indicated that PMCCA films revealed a green color in the oxidized state and a high transmittance in the neutral state. The conductivities of PMCCA are in the range of 10⁻⁵–10⁻⁴ S cm⁻¹.     

Enhancing mechanical and fracture properties of sandwich composites using nanoparticle reinforcement

Polyurethane (PU) foam is reinforced with SiC nanoparticles to develop core materials for sandwich composites. Isocyanate component (Part A) of PU foam was dispersed with SiC nanoparticles, and then mixed with polyol (Part B) to manufacture nanophased core materials. Nanoparticle reinforcement varied from 0.1 to 2.0 wt% of the total polymer. Both pristine and silane functionalized SiC nanoparticles were used in the investigation. Nanophased foams were tested in compression and flexure to determine the mechanical properties. Fracture toughnesses K _IC and G _IC were determined using the SENB test. Sandwich panels were fabricated and tested for face-core debond fracture toughness using the tilted sandwich debond test. The study has revealed that reinforcement of the foam by pristine nanoparticles substantially enhances mechanical properties but degrades fracture toughness. This loss in fracture toughness, however, may be recovered with the use of functionalized nanoparticles. Small concentrations (0.1–0.2 wt%) of functionalized nanoparticles provided large improvement in debond fracture toughness of sandwich specimens.     

Studies on lithium alumino phosphate glasses doped with selenium ions for hard electrolytes

Glass samples of the system (100 − x) (0.5 Li₂O–0.2Al₂O₃–0.3P₂O₅) + xSeO₂ (x is ranging from 0 to 12 mol%, labeled as LAPS _x ) were prepared using the melt quenching technique. FTIR spectral studies indicate that selenium ions mostly occupy network modifying sites due to isolated selenite (SeO₃ ²⁻) groups up to 6 mol% of SeO₂ (LAPS₆) in the LAPS glass network. This has a tremendous effect on the electrical properties. Glass forming ability parameter (K _gl) and the glass transition temperature (T _g) of LAPS samples were characterized by DTA traces. Electrical measurements were carried out as a function of frequency and temperature over the frequency range of 10 Hz to 10⁶ Hz and a temperature range of 303–423 K. The electric modulus formalism was applied to study the relaxation behavior using the impedance data for all the samples at 303 K and also for analyzing the relaxation behavior of the highest conducting sample (6 mol% of SeO₂) at different temperatures. An attempt has been made to relate the measured properties to the structural modifications due to the modifying effect of isolated selenite (SeO₃ ²⁻) groups in the glass network.     

Influence of temperature on the low- and high-frequency relaxation in a TTB-type ferroelectric relaxor Pb2K(Nb0.1Ta0.9)5O15

Dielectric measurements on Pb₂K(Nb_0.1Ta_0.9)₅O₁₅ ceramics have been reported at 140<T<530 K in the 20–10⁹ Hz frequency range. The tetragonal tungsten bronze-type (TTB) material shows a typical ferroelectric relaxor behaviour. Three dielectric dispersions are observed. The relaxor behaviour results from a thermally activated relaxation with a large time distribution. This relaxation could be interpreted in terms of a polar microdomain concept. The two other dielectric dispersions result from a space charge effect and from a relaxation probably related to the TTB structure.     

The mechanical and structural properties of Y1Ba2Cu3O7−x superconductors

Mechanical losses spectroscopy of two superconducting Y₁Ba₂Cu₃O_7–x samples (T _c=93 K) measured at 5, 10, 20 and 30 MHz revealed four peaks. As the frequency of measurement was increased, the peaks shifted to higher temperatures. The relaxation process was found to have an activation enthalpy of 0.188, 0.092, 0.209 and 0.314 eV with an attempt frequency,f _o, equal to 2.46 × 10¹⁵, 5.95 × 10¹⁰, 1.64 × 10¹⁴, and 7.82 × 10¹³ Hz for P₁, P₂, P₃ and P₄ peaks, respectively. The mechanism responsible for these relaxation peaks is discussed. The infrared spectra of some of these compounds provide evidence for oxygen rearrangement on going from tetragonal to orthorhombic phase. X-ray diffraction analysis shows that these compounds correspond to a single phase which is an orthorhombic perovskite structure.     

Spring type conducting polymer actuator working in air

Although major advances in actuator performances have been obtained in the last few years, the actuation of conducting polymer (CP) actuator is still limited to bending movement in liquid electrolyte. It restricts the various application fields of CP actuator. So in this study, spring type CP actuator which can produce linear movement and work in air is prepared. It is composed of two polypyrrole (PPy) films having different actuation mechanism and polyurethane (PU) based solid polymer electrolyte (SPE). Even though the ionic conductivity of PU based SPE is low, the actuation behavior of CP actuator especially working in air is much influenced by the flexibility rather than the ionic conductivity of SPE. Then PU based SPE with high flexibility is used in a spring type CP actuator. The morphology of PPy films, ion conductivity of SPE, actuation movements according to its length and applied voltage and loading ability of actuator were investigated. SPE had a maximum conductivity of 2.20 × 10^?6 S/cm at room temperature for 15 wt% of Mg(ClO₄)₂ salts and the actuator which was fabricated in 21 mm length showed maximum displacement at 12 V. Also it was confirmed that spring type CP actuator could Exhibit 10 MPa of loading ability through the tensile strength test. As a result, solid-state spring type CP actuator having both linear movement and loading ability was demonstrated.     

A novel route for the synthesis of processable conducting poly(m-aminophenol)

Polymerization of m-aminophenol (mAP) in aqueous NaOH solution was done chemically by using ammonium persulfate (APS) as an oxidative initiator. The product poly(m-aminophenol) (PmAP) was found to be highly soluble in aqueous sodium hydroxide, dimethyl sulfoxide (DMSO) and N,N-dimethyl formamide (DMF). From the intrinsic viscosity measurement, the optimum condition for the polymerization was established with 0.6 M NaOH medium with the ratio of monomer to oxidant as 1:1.5 (mol:mol). The polymer was characterized by FTIR and ¹H NMR spectroscopy, elemental (CHNS) and thermogravimetric (TGA) analyses. From the spectroscopic analysis the structure of the polymer was found to resemble that of hydroxy polyaniline as the polymer contains free –OH groups attached to o/m position in the phenyl ring. The elemental analysis of the polymer also confirmed the same. From TGA study, the polymer was found to be thermally stable. A freestanding film of poly(m-aminophenol) was cast in DMSO solution followed by solvent removal and drying of the film at 100 °C for 7–8 h in an oven. A dc conductivity of 4.8 × 10⁻⁴ S cm⁻¹ was obtained for the synthesized polymer film after doping with H₂SO₄ solution.     

Thermal response of a fluid near its critical point:3He atT>T c

The local density response is studied in a simple fluid near the liquid-vapor critical point, subjected to temperature oscillations of its container. This investigation provides a new approach in the study of the adiabatic energy transfer (“piston effect”) in the fluid. The density response functionZ _F (ω, ε,z) is calculated for³He in the absence of stratification, where ω is the angular frequency, ε=(T−T _c )/T _c the reduced temperature,T _c =3.316 K the critical temperature, andz the vertical position in the container. Experiments are described where the density is measured by two superposed capacitive sensors in a cell of 3.5 mm height, and where the temperature oscillation frequencyf=ω/2π is varied between 10⁻⁴ and 2 Hz. Over the experimental range 5×10⁻⁴<ε<5×10⁻² there is in general reasonable agreement between predictions and experiments. The systematic departures might be accounted for by deviations from 1D geometry, which were not included in the calculations. Over the frequency and reduced temperature ranges, the damping effect from the critical bulk viscosity is predicted to be too small to be detectable. The observed effect of the stratification and its frequency dependence inZ _F are briefly discussed. In the appendix, the predicted critical acoustic attenuation from the bulk viscosity is compared with published data, the effect from finite thermal conductivity of the fluid container plates and also the corrections toZ _F for the effects of the cell sidewalls are calculated. F. Pobell     

Synthesis and properties of poly (organophosphazenes) ionomers [NP(HNC6H5)2−(x+y)(HNC6H4SO3H) x (HNC6H4SO3Li) y ] n

Poly(anilino sulphamicphosphazenes) such as [NP(HNC₆H₅)_2–x (HNC₆H₄SO₃H) _x ] _n for polymer (I) x=0.3 and for polymer (II) x=0.8 were prepared by the reaction of poly(anilinophosphazene) [NP(HNC₆H₅)₂] _n and sulphonic chloride HSO₃Cl in tetrachloroethane solvent several timeS. Also, H protons in the polymer (I) and (II) were prepared from lithum hydroxide in aqueous solution. It was found, by chemical analysis, that the product prepared with (I) and (II) had compositions such as [NP(HNC₆H₅)_1.7 (HNC₆H₄SO₃H)_0.1(HNC₆H₄SO₃Li)_0.2] _n (III) and [NP(HNC₆H₅)_1.2(HN-C₆H₄SO₃Li)_0.8] _n (IV). Also, the resistivity of products (III) and (IV) were determined and found to be 3.3×10⁷ and 1.5×10⁷ cm^–1, respectively.     

Viscosity measurements near a critical point using a novel torsion oscillator

A torsion-oscillator viscometer has been constructed for the measurement of the viscosity of fluids near both liquid-vapor and liquid-liquid critical points. This viscometer has a resolution of ±0.2% and operates at a low frequency (0.6 Hz) and a very low shear rate (0.05 Hz). Thus, it can be used closer to critical points than other viscometers before encountering the non-Newtonian phenomena associated with critical slowing down. This viscometer was used to study the viscosity anomaly near the consolute point of mixtures of methanol and cyclohexane along paths of constant pressure and paths of constant volume at temperatures spanning the range 10^–5 < (T-T _c)/T _c<10^–2. The data are consistent with a simple, power-law divergence of the viscosity with a multiplicative background characterized by an apparent exponent y0.041. Recent theoretical estimates for y are near 0.033. If the data are to be fit with the theoretical value of y, one must simultaneously restrict the range of the data and introduce additional unphysical parameters into the fitting function.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

A.c. conduction mechanism and dielectric properties of co-evaporated SiO/B2O3 amorphous thin films

The a.c. electrical properties on Al-SiO/B₂O₃-Al sandwich devices with various compositions of SiO/B₂O₃ were studied over a frequency range of 2×10² to 1×10⁶ Hz and in the temperature range 158 to 463 K. The a.c. conductance G varies with frequency according to the relation G ^s, where the exponent s was found to be 0.92 (at 158 K) in the frequency range 8×10² to 2×10⁴ Hz and above 10⁵ Hz the conductance shows a square law dependence on frequency. These results suggest that the a.c. conduction mechanism in SiO/B₂O₃ thin films is due to an electronic hopping process. The numbers of localized sites were calculated using the conductivity relations given by Elliott and by Pollak and the results are compared. The effects of composition, temperature and annealing on the dielectric constant and loss factor were studied. The relative dielectric constant and loss factor were found to decrease with the increase of B₂O₃ content in SiO. Annealing of the samples reduces the values of the dielectric constant, loss factor tan , temperature coefficient of capacitance and a.c. conductivity. The variation in capacitance with the composition of SiO/B₂O₃ was investigated at room temperature, the results being normalized to 10 kHz. The dispersion was found to decrease with the addition of B₂O₃ into SiO.     

Ionic conductivity of fluoroaluminoindate glasses

(54 - 2.4x)InF₃ + xA1F₃ + (36 -1.6x)BaF₂ + 3xPbF₂ + 1OLiF glasses (nine compositions,x varying from 0 to 18 mol % at 2.25 mol % intervals) were prepared. The glass compositions were taken between the 60InF₃ + 40BaF₂ and 25A1F₃ + 75 PbF₃ eutectics, of which the former is glass-forming (10 mol % LiF was added for glass stabilization). The electrical properties of the glasses were studied by impedance spectroscopy at frequencies from 5 Hz to 500 kHz and temperatures from 20 to 200‡C. The 400-K ionic conductivity of the glasses was found to rise from 4.3 x 10^-6 S/cm in the PbF₂-free glass to 1.4 x 10^-5 S/cm in the glass containing 54 mol % PbF₂; concurrently, the 300-K static dielectric permittivity increases from 17 to 29.