Structure and dielectric properties of highly (100)-oriented PST thin films deposited on MgO substrates

High-quality Pb_0.4Sr_0.6TiO₃ (PST) thin films have been epitaxially grown on MgO (100) substrates at various substrate temperatures by the pulsed laser deposition (PLD) technique. Their crystalline phase structures and surface morphology were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their in-plane orientation was observed by the Phi scans on the (111) plane. Their dielectric properties were measured by a precision impedance analyzer. Results show that the perovskite phase was stable in PST thin film. The crystalline phase formation of the thin film depended on the deposition temperature. The phase formation ability and (100)-orientation of these films were increased with increasing deposition temperature. Both of the high tunabilities and low dielectric loss of the thin films show that the (100)-oriented PST is a potential material that can be used for tunable applications.     

Giant pyroelectric coefficient of Mn-doped PLT thin films epitaxially grown on (001) Pt/MgO

The c-axis-oriented epitaxial thin films of Mn-doped Pb_1−xLa_xTi_1−x/4O₃ (PLT) on (001) Pt/MgO substrates were prepared by rf-magnetron sputtering. To investigate the effect of the doped ion, 0-1.7 mol% MnO₂ added to the PLT target powder. The temperature dependence of the relative dielectric constant ?_r measurements and modified Curie-Weiss plots suggested that the increasing of diffuseness n was induced by high-La substitution and the diffuseness n of PLT thin films decreased by the addition of Mn, considerably. Inner stress and thermodynamic analysis were carried out and the results propose that the increasing of γ with Mn doping caused by increasing the misfit strain of the c-axis-oriented epitaxial PLT thin films and substrate. As a result, giant pyroelectric coefficient (γ = 15.8 × 10⁻⁸ C/cm² K) of Mn-doped epitaxial PLT thin film was achieved.     

(K,Na)NbO3基无铅压电陶瓷的研究现状与进展

综述了近年来(K,Na)NbO3基无铅压电陶瓷在掺杂改性以及晶粒定向技术制备织构化陶瓷研究的新进展,重点分析了(K,Na)NbO3基无铅压电陶瓷的K/Na比为0.5和非0.5时,陶瓷压电性能上的差异,发现K/Na比偏离0.5时,具有更为优异的压电、介电性能,最后展望了(K,Na)NbO3基无铅压电陶瓷的掺杂改性及晶粒定向技术的研究趋势.     

Barium titanate thin films deposited by electrophoresis on p-Doped Si (001) substrates

Barium titanate (BaTiO3) thin films have been prepared by electrophoretic deposition on p-doped and platinum covered silicon (Si) substrates. Their structure, nanostructure and dielectric properties were characterized. The as-deposited films were polycrystalline and composed by barium titanate nanograins with an average grain size approximately 9 nm. Annealing at high temperatures promoted grain growth, so that the samples annealed at 600 degrees C presented average grain sizes approximately 24 nm. From Raman spectroscopy measurements it was found that the tetragonal (ferroelectric) BaTiO3 phase was stabilized on the films. Also, at higher annealing temperatures, cation disorder was reduced on the films. From measurements of the temperature dependence of the dielectric permittivity the corresponding paraelectric-ferroelectric phase transition was determined. The observed transition temperature (approximately 100 degrees C) was found to be below the BaTiO3 bulk or thick film values, due to the small nanosized grains composing the films.     

Piezoelectric Properties of （Na0.5K0.5-xLix）NbO3 Ceramics

Lead-free piezoelectric ceramics （Na0.5K0.5-xLix）NbO3 （x=0.057-0.066） were synthesized by an ordinary sin-tering technique. Substituting Li for K can lead to structural distortion, which improves the Curie temperature （To） greatly. By adding appropriate LiNbO3 content, piezoelectric constant d33 values reach 202-212 pC/N. Electromechanical coefficients of the planar mode reach 44.4%-46.8%. The dielectric loss is below 2.6%, which is much lower than reported （about 50%）. The To of （Na0.5K0.5-xLix）NbO3 （x=0.057-0.066） is in the range of 490-510℃, at least 70℃ higher than that of pure （Na0.5K0.5）NbO3 ceramics. The results show that （Na0.5K0.5-xLix）NbO3 ceramic is a kind of good lead-free high-temperature piezoelectric material.     

（K，Na）NbO3基无铅压电陶瓷及其应用研究进展

随着人类社会可持续发展战略的全面实施.(K,Na)NbO3基无铅压电陶瓷以其优越的压电性能和较高的居里温度受到人们的广泛关注.分析并评述了其国内外的研究及应用近况,(K,Na)NbO3基无铅压电陶瓷在改性方面取得了较大的进展,但总体上还不能与铅基体系相媲美.因此,(K,Na)NbO3基体系的性能和应用要达到铅基压电陶瓷的水平还需进行大量的研发工作.     

Lead-free (K,Na)NbO3 thin films derived from chemical solution deposition modified with EDTA

Potassium sodium niobate is an important and promising functional material due to its ferroelectric, piezoelectric, and pyro-electric properties, and have received much attention for decades. In this paper, lead-free (K, Na)NbO₃ (KNN)-based ferroelectric thin films were successfully prepared by a chemical solution approach using Nb₂O₅ as niobium resource instead of the expensive niobium ethoxide. The films with a pure perovskite phase were obtained by such an approach modified with ethylenediaminetetraacetic acid (EDTA). EDTA plays a positive role in suppressing the volatilization of alkali metal and facilitates a better film growth rate. EDTA introduction prevents the formation of the pyrochlore phase. The films synthesized with EDTA show large grains and good crystallization, indicating decreased nucleation temperature. The obtained KNN thin films exhibit low leakage current, large saturated polarization, and small coercive field. These results are attributed to the added EDTA, which is effective in inhibiting the formation of vacancies, and to the weakened effect of the defect pinning or clamping of domain walls.     

Epitaxially grown molybdenum thin films deposited by laser ablation on (100) MgO substrates

We report here on the deposition process by laser ablation and on the characterization of molybdenum films epitaxially grown on (100)MgO single-crystal substrates. The 50 nm (100)Mo films are epitaxied. These films have a low resistivity (5.3 μΩ cm at 273 K) close to the pure molybdenum resistivity value (4.85 μΩ cm at 273 K). The low resistivity corroborates the quality of the Mo films in spite of a very low deposition rate (25 nm h⁻¹). An other orientation has been also encountered. The complementary characterization methods (X-ray diffraction in θ-2θ or oscillating crystal mode, reflection high-energy electron diffraction and electron channelling patterns) have shown it to be the (110)Mo orientation.     

Growth and structural investigations of epitaxial hexagonal YMnO3 thin films deposited on wurtzite GaN(001) substrates

Epitaxial hexagonal YMnO₃ (h-YMnO₃) films having sharp (00l) X-ray diffraction peaks were grown above 700 °C in 5 mTorr O₂ via pulsed laser deposition both on as-received wurtzite GaN/AlN/6H-SiC(001) (w-GaN) substrates as well as on w-GaN surfaces that were etched in 50% HF solution. High-resolution transmission electron microscopy revealed an interfacial layer between film and the unetched substrate; this layer was absent in those samples wherein an etched substrate was used. However, the substrate treatment did not affect the epitaxial arrangement between the h-YMnO₃ film and w-GaN substrate. The epitaxial relationships of the h-YMnO₃ films with the w-GaN(001) substrate was determined via X-ray diffraction to be (001)_YMnO3 ‖ (001)_GaN : [11¯0]_YMnO3 ‖ [110]_GaN; in other words, the basal planes of the film and the substrate are aligned parallel to one another, as are the most densely packed directions in planes of the film and the substrate. Interestingly, this arrangement has a larger lattice mismatch than if the principal axes of the unit cells were aligned.     

Structural properties of epitaxial SrCuO2 thin films on SrTiO3 (001) substrates

Thin films of SrCuO₂ with tetragonal structure have been epitaxially grown on SrTiO₃ (001) substrates by high-oxygen pressure sputtering technique. The interface structure between SrCuO₂ and SrTiO₃ and configuration of defects in SrCuO₂ thin films have been characterized by means of high-resolution transmission electron microscopy. Two types of film-substrate interface structure coexist and are determined as bulk-SrO-TiO₂-Sr(O) -CuO₂-Sr-bulk and bulk-SrO-TiO₂-SrO-Sr(O) -CuO₂-Sr-bulk. The planar faults with double SrO atomic layers in {100} planes in SrCuO₂ thin films are observed, which mainly arise from the coalescence of these two types of film-substrate interface structure. Meanwhile, planar faults in {110} planes are observed in thin films and structural models are proposed.     

Ferroelectric BiFeO3-PbTiO3 thin films on Pt/Si substrates

In this work we report on the preparation and properties of bismuth ferrite lead titanate films [(1- x)BiFeO(3-x)PbTiO3] with tetragonal compositions (x = 0.8 and 0.7) and compare them with compositions close to the morphotropic phase boundary (MPB; x = 0.4 and 0.3). The films were prepared by pulsed laser deposition on Pt/Si substrates, and exhibited a dense columnar grain growth. X-ray diffraction analysis revealed that the films have a perovskite structure with a preferred (111) texture. The dielectric properties, polarization-field hysteresis, and leakage current behavior of the films is also reported. For MPB compositions, the films exhibited remanent polarizations with 2Pr up to 100 microC cm(-2) and E(c) approximately 185 kV cm(-1) under a maximum applied field of 500 kV cm(-1), while the tetragonal compositions exhibited 2Pr values in the range of 45-52 microC cm(-2) with a coercive field E(c) approximately 118 kV (-1).     

Growth, structural and electrical properties of polar ZnO thin films on MgO (100) substrates

ZnO films have been grown on (100) oriented MgO substrates by pulsed-electron beam deposition in the room temperature to 500 °C range. Highly (00·2) textured films are obtained for a growth temperature higher than 200 °C, and epitaxial films are formed at 500 °C with the following epitaxial relationships: (1-1·0)_ZnO // (110)_MgO and (11·0)_ZnO // (110)_MgO, despite the difference in symmetry between film and substrate. The low temperature resistivity curves evidenced a metal-semiconductor transition for the ZnO films grown in the 300 to 500 °C range which has been interpreted in the frame of the model of conductivity in disordered oxides.     

Capacitance of (001)SrRuO3/(001)SrTiO3 and (110)SrRuO3/(110)SrTiO3 interfaces in epitaxial heterostructures grown on LaAlO3 substrates

The temperature dependence of the permittivity ? measured at T = 120?300 K for SrTiO₃ layers in SrRuO₃/SrTiO₃/SrRuO₃ heterostructures grown on (001)-and (110)-oriented LaAlO₃ substrates is well approximated by the relation ?₀/? = C ₀ ^?1 (T ? T _CW) + ?₀/?_I, where the C ₀ and T _CW values virtually coincide with the Curie constant and the Curie-Weiss temperature, respectively, for SrTiO₃ single crystals. The specific capacitance of the (001)SrRuO₃/(001)SrTiO₃ and (110)SrRuO₃/(110)SrTiO₃ interfaces calculated using the obtained ?_I values is 2.7 and 6.4 μF/cm², respectively.     

(K0.5Na0.5)NbO3-LiNbO3无铅压电陶瓷的烧结特性和压电性能研究

采用传统陶瓷烧结工艺制备了(1-x)(K0.5Na0.5)NbO3-xLiNbO3无铅压电陶瓷,研究了陶瓷的结构、烧结特性及电性能特征.制备的(K0.5Na0.5)NbO3-LiNbO3陶瓷为单一的钙钛矿结构,室温下其相结构随LiNbO3含量增加逐渐由正交相向四方相转变,显微结构也由于LiNbO3含量的不同而表现出很大差异.与(K0.5Na0.5)NbO3陶瓷相比,(K0.5Na0.5)NbO3-LiNbO3陶瓷的烧结温度降低,烧结特性得到改善. (K0.5Na0.5)NbO3-LiNbO3陶瓷表现出优越的压电性能,其中0.94(K0.5Na0.5)NbO3-0.06LiNbO3(x=0.06)陶瓷的压电常数d33达到205pC/N,机电耦合系数kp为40.3%,kt达到49.8%.     

Elasto-plastic properties of gold thin films deposited onto polymeric substrates

This work examines mechanical properties of 50–300 nm gold thin films deposited onto micrometer-thick flexible polymer substrates by means of tensile testing of the film–substrate system and modeling. The film properties are extracted from mechanical testing of the film–substrate system and modeling of the bimaterial. Unlike materials in bulk geometry, the film elastic modulus and yield strength present an important dependence with film thickness, with modulus and yield strength of about 520 and 30 GPa, respectively, for the thinner films and decreasing toward the bulk value as the film thickness increases. The relation between grain size, film thickness, and yield strength is examined. Finite element analysis provides further insight into the stress distribution in the film–substrate system. L. Llanes—MS student at ITM, Merida, Mexico.     

Investigation of structural properties of ITO thin films deposited on different substrates

The influence of the substrate nature on the structure and morphology of ITO thin films grown by thermal evaporation in vacuum is investigated. The as-prepared metal films with Sn/In molar ratio of 0.1 were subsequently annealed for 2 h at 723 K in air (to obtain tin doped indium oxide), then annealed in vacuum at 523 K, followed by UV irradiation (to reduce the electrical resistivity). Irrespective of substrate nature, XRD data evidence a (222) preferential orientation in films. Substrate nature, annealing in vacuum and UV irradiation influence the structure, morphology, optical, electrical and surface wetting properties of the films' surface.     

Structural and magnetic properties of CoFe2O4 thin films deposited by laser ablation on Si (001) substrates

Cobalt ferrite (CoFe₂O₄) thin films have been deposited on Si (001) substrates, with different substrate temperatures (T_dep = 25 °C − 600 °C). The films were prepared by pulsed laser ablation with a KrF excimer laser (wavelength λ = 248 nm). The oxygen pressure during deposition was 2 × 10⁻² mbar. The films structure was studied by X-ray diffraction (XRD) and their surface was examined by scanning electron microscopy (SEM). The magnetic properties were measured with a vibrating sample magnetometer (VSM). For low deposition temperatures, the films presented a mixture of a CoFe₂O₄ phase, with the cubic spinel structure, and cobalt and iron antiferromagnet oxides with CoO and FeO stoichiometries. As the deposition temperature increased, the CoO and FeO relative content strongly decreased, so that for T_dep = 600 °C the films were composed mainly by polycrystalline CoFe₂O₄. The magnetic hysteresis cycles measured in the films were horizontally shifted due to an exchange coupling field (H_exch) originated by the presence of the antiferromagnetic phases. The exchange field decreased with increasing deposition temperature, and was accompanied by a corresponding increase of the coercivity and remanence ratio of the cycles. This behavior was due to the strong reduction of the CoO and FeO content, and to the corresponding dominance of the CoFe₂O₄ phase on the magnetic properties of the thin films.     

Growth temperature dependent dielectric properties of BiFeO3 thin films deposited on silica glass substrates

We have studied the dependence of dielectric properties on the deposition temperature of BiFeO₃ thin films grown by the pulsed laser deposition technique. Thin films have been grown onto amorphous silica glass substrates with pre-patterned Au in-plane capacitor structures. It is shown that on the amorphous glass substrate, BiFeO₃ films with a near-bulk permittivity of 26 and coercive field of 80 kV/cm may be grown at a deposition temperature of about 600 °C and 1 Pa oxygen pressure. Low permittivity and higher coercive field of the films grown at the temperatures below and above 600 °C are associated with an increased amount of secondary phases. It is also shown that the deposition of BiFeO₃ at low temperature (i.e. 500 °C) and post deposition ex-situ annealing at elevated temperature (700 °C) increases the permittivity of a film. The applied bias and time dependence of capacitance of the films deposited at 700 °C and ex-situ annealed films are explained by the de-pinning of the ferroelectric domain-walls.     

Structure and optical properties of thin titanium films deposited on different substrates

Thin films of titanium were deposited on different substrates at room temperature. Measurements were made of the optical constants and of the transmittance of titanium films evaporated on to fused quartz. Films of titanium 10 to 40 nm thick were found to have quite uniform transmittance throughout the visible spectrum. Because titanium getters strongly during its evaporation, pure and compact titanium films can only be produced by fast evaporation under extremely good vacuum conditions. All films prepared for optical measurements, for X-ray and for scanning electron microscopy studies were, therefore, deposited at a pressure 10^–4 Pa and with deposition rate 4 nm sec^–1. The measurements were made using a Beckman double-beam spectrophotometer UV 5230, Siemens D 500 X-ray diffractometer, and SEMCO nanolab 7 scanning electron microscopy.