Effects of plasticization on the piezoelectric properties of nylon 11 films

Nylon 11 films (-form) were plasticized by immersion in 2-ethyl 1,3 hexanediol. Two different kinds of studies were performed. In the first study, poled nylon 11 films were plasticized by immersion in the plasticizer for different lengths of time. The piezoelectric strain constant,d ₃₁, initially increased up to a plasticizer content of 14% (by weight) and then decreased. The values of piezoelectric stress constant,e ₃₁, however, decreased with increase in dipping time. In the second study, the films were initially plasticized and then poled. Bothd ₃₁ ande ₃₁ were higher for plasticized films compared to unplasticized films under identical poling conditions. X-ray diffraction studies showed some conversion of -phase to -phase during the process of plasticization.     

Structure and optical properties of vacuum-deposited scandium films on crystalline substrates

Thin films of scandium have been deposited in high vacuum on to amorphous and crystalline substrates at room temperature. These films were examined by X-ray diffraction and transmission electron microscopy to study the structure and orientation of films of various thicknesses. It was observed that thin scandium films evaporated on to air-cleaved mica and rocksalt substrates have a polycrystalline structure. The variation of the refractive indexn, the extinction coefficientk and optical conductivity ₁ () with wavelength were studied. Measurements were made in the spectral region from 2.5 to 40m.     

Structural studies of nylon 13,13

A structural study of nylon 13,13 has been carried out by means of X-rays and electron microscopy. Both X-ray and electron diffraction data, obtained from oriented films as well as from lamellar crystals prepared in solution, evidenced that nylon 13,13 adopts a structure in a monoclinic lattice of parameters a _o=0.488 nm, b _o=0.473 nm, c _o=3.40 nm, ==90°, =121°. As expected from the constitution of the nylon, no trace of structure with chains in fully extended conformation (-form) was observed throughout this study.     

Cooper pair breaking and isotope effect coefficient variation in high-Tc superconductors

The effect of pair breaking on the isotope effect coefficient=–d lnT _c/d lnM in La_2–x Sr _x CuO₄ and Pr-, Ca-, and Zn-doped YBa₂Cu₃O_7–x and EuBa₂Cu₃O_7–x is studied using the generalized Abrikosov-Gorkov theory recently employed by Singh and Kishore for superconductivity. It is argued that the isotope effect coefficient can be further enhanced, in agreement with experimental observations, by considering the dependence of the characteristic scattering time _s for Cooper pairs on the concentrationn of impurities (both magnetic and nonmagnetic) and the disorder ignored by them (J. Supercond. 8, 9 (1995).     

Coefficients for equilibrium partition of a third element between solid and liquid in iron-carbon base ternary alloys and their relation to graphitization during iron-carbon eutectic solidification

During iron-carbon eutectic solidification, the coefficients for partition of a third element between the eutectic liquid and its solid were evaluated thermodynamically. The coefficientk _M ^A/L for the equilibrium partition of the third element (M) between austenite and liquid iron largely depended on the interaction between carbon and the third element and a simplified method for the evaluation ofk _M ^A/L was introduced. The coefficients,K ^S andK ^M, for the partition of the element between the eutectic liquid and its solid in the stable and metastable eutectic solidification, respectively, were also calculated fromk _M ^A/L and the coefficientk _M ^C/A for the equilibrium partition of the element between cementite and austenite. It was indicated by the thermodynamics of the free energy for the co-existing phases that the effect of a third element on graphitization occurring during eutectic solidification was related quantitatively to the value of K which was represented byK ^S-K ^M. The effect of a third element on the difference between the stable and metastable eutectic temperatures and on the carbon activity of liquid iron was closely related to K or the equilibrium partition coefficient,k _M ^C/A .     

Size effect in the low-field Hall coefficient of single-crystal copper films

Measurements of the low-field Hall coefficientR _H of single-crystal copper films were made at 4.2 K by the use of a SQUID. The surface normaln of the samples was directed in the [100], [110], and [111] directions and the ratio of the thickness to the mean free path ranged from 0.1 to 0.7. It is found that the effect of surface scattering causesR _H to decrease whenn [100], whereas it causesR _H to increase whenn [110] and [111]. This behavior is interpreted in terms of the geometrical characteristics of the Fermi surface.     

Electro-mechanical behaviour of single domain single crystals of bismuth titanate (Bi4Ti3O12)

The piezoelectric constantsd ₁₁,d ₂₂ andd ₃₃ for a single domain single crystal of Bi₄Ti₃O₁₂ have been measured at room temperature using appropriate crystal cuts on a Berlincourtd ₃₃ meter. From the known temperature dependence of the spontaneous polarization, lattice strain and dielectric permittivity, the equivalent piezoelectric constants have been calculated assuming a simple proper ferroelectric in which,P _s, is the order parameter. Constants in the plane of the perovskite-like sheets in the Bi₄Ti₃O₁₂ structure (d ₁₁,d ₂₂) show good agreement with experimental values. The calculated value of the constantd ₃₃ is more than an order of magnitude larger than the experimentally-measured value and gives clear indication of the indirect coupling to the strain in the tetrad axial direction and the need for a more sophisticated phenomenology.     

Electrical properties of ZnSe-CdS alloy films

Thin films of ZnSe _x CdS_1–x (t 0.6 m) over the entire range of x, were deposited on glass substrates at two temperatures, T _s (350 and 470 K) by vacuum evaporation. X-ray diffraction studies showed that all the films were polycrystalline in nature. Films prepared at 470 K were nearly stoichiometric. Grain size increased with substrate temperature, T _s. The electrical conductivity and Hall measurements were carried out by d.c. van der Pauw technique. Hall effect studies/hot probe test showed that all the films were of n-type conductivity. Hall mobility increased with T _s. In addition, mobilities increased with temperature in films of all compositions, indicating the dominance of grain-boundary scattering. Grain-boundary potentials were in range 0.03–0.06 eV.     

Electrical resistivity of polycrystalline vanadium films

The electrical resistivity of polycrystalline vanadium films (20 to 400 nm thick) deposited on to amorphous and crystalline substrates heated to 473 K during deposition was studied. The data were interpreted in terms of the classical size effect for thick films. The mean free path,I ₀, the average resistivity, ₀, and the density of conduction electrons,N, were calculated. These values are compared with those found in earlier works.     

Magnetic properties,microstructures and domain structures of arc-plasma sprayed Nd-Fe-B permanent magnet

Thin Nd-Fe-B films prepared by arc-plasma spraying at different substrate temperatures were investigated for their magnetic and structural properties. The isotropic magnets with the best magnetic properties (_M H _c=1.2 MA m^–1, _o M _r=0.6 T, (BH)_max=64 kJ m^–3), were obtained after plasma spraying the Nd-Fe-B powders on water-cooled copper substrates and subsequently annealing the films for 0.5 h at 750 °C. The optimum magnetic properties of the anisotropic Nd-Fe-B films, i.e. _M H _c=1.2 MA^–1, _o M _r=0.9 T and (BH)_max=180 kJ m^–3, were obtained in films sprayed on to heated to 600 °C substrates. The magnetic properties of the sprayed films were strongly influenced by the microstructure. The domain structure of these films is also presented.     

4He Confined in 0.0483 μm Planar Geometry, Specific Heat and Scaling Near Tλ

The phonon diffusiveness coefficient D related to scattering of phonons by point mass defects embedded in cubic crystalline media can be written as product of diffusiveness coefficient for a corresponding reference isotropic medium D _is , and the dimensionless coefficient which depends on two dimensionless elastic parameters s ₂ , s ₃. This coefficient is studied in the triangle–shaped region of plane (s ₂ ,s ₃ ) in which cubic elastic crystalline media are mechanically stable. As a function of s ₂ and s ₃ the coefficient is nonmonotoneous and behaves singularly on the line s ₂ = s ₃. The underlying physical mechanism is considered.     

Piezoelectricity and polarization studies in unstretched san copolymer films

The piezoelectricity and charge storage in unstretched corona poled poly (styrene-co-acrylonitrile) films have been investigated under different poling conditions. The piezoelectric coefficient d₃₁ has been measured as a function of poling field (E_p) and poling temperature (T_p) and the maximum value of d₃₁ 1.0 pC/N has been obtained at E_p 46 MV/m and T_p = 85 °C. The Frolich equation for dipolar polarization has been applied for quantitative analysis of the thermally stimulated current (TSC). The g-factor = 1.7 has been obtained, suggesting cooperative dipolar relaxation. The Young's modulus has been measured to be 0.45 GPa. The dipolar polarization from the TSC and the elastic modulus of the films have been correlated to the piezoelectricity through the modified equation for d₃₁ for amorphous SAN films. It has been concluded that the mechanisms of the dimensional and the local field effects are involved in the piezoelectric phenomenon.     

Effect of Composition Variations on Electrical and Optical Properties of La1−x (Ca, Sr) x MnO3 Thin Films

Thin films of La _0.67 Ca _0.33 MnO ₃₊ (d 200 nm) grown at 750° C on MgO(100) substrates by pulsed laser deposition were annealed in various oxygen atmospheres. The LaF ₃ , CaF ₂ and Mn overlayers (d 5-10 nm) have been evaporated onto the films in order to saturate the compound by La, Ca or Mn during subsequent annealing at 900° C in air. Further, the pulsed injection CVD method has been utilized to prepare series of La _1–x Sr _x MnO ₃ films with x = 0÷0.5 on LaAlO ₃ (100). The effect of composition variations on electrical resistivity and magnetoresistance of the films as well as on their optical transmission and reflection spectra in the energy range between 0.2 and 4.0 eV has been investigated.     

Effect of composition on optical properties of co-evaporated Mn/SiO x,Cr/SiO x and Cu/SiO x cermet thin films

Optical absorption spectra of amorphous Mn/SiO _x , Cr/SiO _x , and Cu/SiO _x cermet films, 300 nm thick, with compositions from 0 to 25 at% Mn, Cr and Cu, respectively, prepared by co-evaporation at 293 Kin vacuo have been investigated. The linearity of ()^1/2 versus graphs in the high absorption region for all the cermet films indicates that indirect photon transitions in k-space are involved in the absorption process. Taue's rule is also confirmed. In all cases the optical energy gap decreases significantly with increasing metallic content of the films and the width of the tail of localized states increases.     

Piezoelectric properties of collagen-nanocrystalline hydroxyapatite composites

In this paper we did a study of the physicochemical, dielectric and piezoelectric properties of anionic collagen and collagen-hydroxyapatite (HA) composites, considering the development of new biomaterials which have potential applications in support for cellular growth and in systems for bone regeneration. The piezoelectric strain tensor element d ₁₄, the elastic constant s ₅₅, and the dielectric permittivity ₁₁ were measured for the anionic collagen and collagen-HA films. For the collagen-HA composite film (Col-HACOM) the main peaks associated to the crystalline HA is present. For the nanocrystalline composite, nanometric HA powder (103 nm particle size) (HAN), obtained by mechanical milling were used. For the composite film (Col-HAN) the HA and CaH(PO₄)₂H₂O phases were detected. One can see that the HA powder (HAN) present the main peaks associated to crystalline HA. The IR spectroscopy measurements on HA-COM and HAN powders, Col-HACOM and Col-HAN composite films and collagen film (Col) presents the main resonances associated to the modes of (PO₄)^3–, (CO₃)^2–. The IR spectra of Collagen Film (Col) shows the bands associated to amide I (C=O), amide II (N–H) and amide III (C–N) vibrational modes. The scanning electron photomicrography of the Col-HACOM and Col-HAN films, respectively, shows deposits of HA on the surface of collagen. It also shows that HACOM crystals has a dense feature, whereas the HAN crystals has soft porous surface. Energy-dispersive spectroscopy (EDS) analysis showed that the main elements of the hybrid sponge were carbon, oxygen, calcium, and phosphorus. The EDS of HACOM crystal, present in the Col-HACOM composite showed a molar ratio Ca/P = 1.71, whereas the Col-HAN composite the molar ratio of calcium and phosphorus (Ca/P = 2.14) and the amount of carbon were greater. The piezoelectric strain tensor element d ₁₄ obtained for the anionic collagen was around 0.102 pC/N. The collagen composite with nanocrystalline HA crystals (Col-HAN) present a better result (d ₁₄ = 0.040 pC/N) compared to the composite with the commercial ceramic (d ₁₄ = 0.012 pC/N). This is an indication that the nanometric particles of HA present little disturbance on the organization of the collagen fibers in the composite. In this situation the nanometric HA are the best candidates in future applications of these composites.     

Dependence of microwave surface resistance on the structure of laser-deposited YBa2Cu3O7?x thin films

The effect of the structure YBa₂Cu₃O_7-x superconducting thin films on microwave surface resistance was investigated. The electon channeling patterns (ECPs) and X-ray experimental results showed that the microwave surface resistanceR _s is strongly correlated with the perfection of the thin films. The films were deposited on LaAlO₃(100) and YSZ(100) substrates. For thin film withR _s of 280, the crystallinity of the thin film shown byw-scanning and-scanning was excellent and the ECPs were very sharp. For thin film with highR _s of 98 m, only bands from the major zone were visible in the ECPs, which suggested poor crystallinity of the film. From this investigation it was shown that the more perfect the thin films, the lower theR _s.     

Optical properties of tin in the 2.5 to 40μm region

The optical constantsn andk of evaporated tin deposited on different substrates (potassium bromide and mica-sheet discs) were determined in the 2.5 to 40m region by measuring its transmittance. From these values a second step vveacarried out to determine other physical parameters of tin films. These were the density of conduction electrons,N, the effective collision frequency of the electrons ₀ the plasma frequency, ₀, the velocity on the Fermi surface,V ₀ the effective area of the Fermi surface,A _eff, and the absorption coefficient,A. The energy-loss functions for surface and volume plasmons show sharp peak at 7.69m. These values are compared with those found in earlier work.     

Poling process and piezoelectric properties of lead zirconate titanate/sulphoaluminate cement composites

The sulphoaluminate cement was, for the first time, used to fabricate 0-3 piezoelectric composites by compressing technique. The dependences of piezoelectric properties of composites on poling conditions, particle size and contents of Lead Zirconate Titanate (PZT) were discussed especially. The results show that the piezoelectric properties of composites are improved by increasing poling field E, poling time t and poling temperature t. The optimum E, t and T are 4.0 kV/mm, 45 min and 120°C respectively in this work. The piezoelectric strain factor d₃₃ is found to increase with increasing particle size of PZT. When the particle size of PZT is larger than about 130 m, the d₃₃ is nearly independent of particle size. The d₃₃, g₃₃ and the electromechanical coupling coefficient K _p, K _t of composites increase rapidly with increasing content of PZT. When the content of PZT reaches 85%, K _p and K _t are 28.54 and 28.19%, respectively.     

Superconducting critical temperature in disordered tin and lead

Three-micrometer-thick tin and lead films were irradiated at temperatures below 7.2K with 25-MeV oxygen ions. The radiation-induced residual resistivity _B , superconducting critical temperature T _c , and transition width T were measured as a function of dose and subsequent thermal annealing. For tin it is found that T _c is mainly a function of _B with the detailed nature of the defects being of minor importance. Quantitative agreement with theory is obtained considering two effects: an enhancement of the isotropic part of the electron-phonon interaction and a smearing out of its anisotropic part with decreasing mean free path of the electrons. For lead the change of T _c depends on the defect configuration and it is shown that dislocation loops produce a significant T _c increase. A possible phonon contribution to T _c due to different vibrational modes of the radiation-induced defects and the host is discussed.This work received financial support from the Bundesministerium für Forschung and Technologie.     

Study of the piezoelectricity in iron-doped collagen films

In this paper a study was carried out of collagen membranes prepared with iron as an impurity. In this study the function of the iron in the collagen structure was examined with the aim of increasing the value of the piezoelectric strain tensor element d ₁₄. We prepared different samples with different iron doping levels. Doped samples by immersion in solutions of FeCl₂ (0.1 M and 0.2 M), FeCl₃ (0.1 M) and FeNH₄SO₄ (0.1 M) and iron doped directly in solution with Fe₂O₃ at 5% and 15% were examined. Mössbauer spectroscopy, the piezoelectric strain tensor element d ₁₄ the elastic constant s ₅₅, and the dielectric function ₁₁ of the samples were examined. The loss factor Q ^–1 of the samples was also measured using the admittance resonance method. The role played by the iron in the different situations and the consequences for the transport properties are discussed.