Preparation and characterization of sol–gel derived (1 0 0)-textured Pb(Zr,Ti)O3 thin films: PbO seeding role in the formation of preferential orientation

Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary region were deposited onto Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates using a sol–gel method. A seeding layer was introduced between the most underlying surface of the PZT film and the platinum electrode surface to control the texture of the PZT thin film. The lead oxide seeding layer resulted in the formation of a single-phase perovskite and absolutely (1 0 0)-textured PZT film. SEM, XRD, XPS, and AES were used to characterize the evolution of the lead oxide layer and the PZT thin films. The growth kinetic mechanism of the (1 0 0)-textured PZT thin films was proposed phenomenologically. The ferroelectric and piezoelectric properties of the PZT films were also evaluated and discussed in association with different preferential orientations.     

Surface modification of NiTi/PZT heterostructure thin films using various protective layers for potential MEMS applications

The present study explored the in-situ deposition of hard and adherent nanocrystalline protective coatings on NiTi/PZT/TiO_x thin film heterostructure prepared by dc/rf magnetron sputtering. Protective layers (AlN, CrN and TiCrN) of approximate thickness (~ 200 nm) were used to improve the surface, mechanical and corrosion properties of NiTi/PZT/TiO_x heterostructure without sacrificing the shape memory effect and ferroelectricity of the NiTi and PZT layers, respectively. The influence of the protective layer on structural, electrical and mechanical properties of NiTi/PZT/TiO_x heterostructure was systematically investigated and the results were compared. Nanoindentation studies were performed at room temperature to determine the hardness and reduced modulus. The surface modified NiTi/PZT/TiO_x heterostructures were found to exhibit high hardness, high elastic modulus and thereby better wear resistance as compared to pure NiTi/PZT/TiO_x films. From the results of potentiodynamic polarization test conducted in 1 M NaCl solution, the CrTiN coated NiTi/PZT/TiO_x heterostructure showed the best corrosion resistance with the lowest corrosion current density (1.52 × 10^? 8 A cm^? 2) and the highest protective efficiency (96.8%). The results presented here prove the potential of a surface modified NiTi/PZT/TiO_x heterostructure to be used in various microelectromechanical (MEMS) applications.     

Shifting of the morphotropic phase boundary and superior piezoelectric response in Nb-doped Pb(Zr, Ti)O3 epitaxial thin films

A shift of the morphotropic phase boundary (MPB) and a superior piezoelectric response are observed in Nb-doped Pb(Zr_xTi_1?x)O₃ (PNZT) thin films epitaxially grown on Nb-doped SrTiO₃(1 0 0) (Nb:STO) substrates. X-ray diffraction and Raman spectra characterizations confirm that a phase transition from a tetragonal structure to a rhombohedral structure occurs when the Zr/Ti ratio varies from 20/80 to 80/20. The phenomenological theory and experimental analyses suggest that the MPB of epitaxial PNZT thin films is shifted to the higher Zr/Ti ratio (around 70/30) from the conventional ratio (52/48) due to the misfit compressive stress induced by the substrate. A maximum local effective longitudinal piezoelectric coefficient (d₃₃) up to 307 pm V^?1 is observed at a Zr/Ti ratio of 70/30 in the current compositional range, again confirming the shifting of MPB in epitaxial PNZT thin films. These findings offer a new insight for the fabrication of epitaxial PZT thin films at MPB with a superior piezoelectric response.     

Highly (1 0 0)-textured Pb(Zr0.52Ti0.48)O3 film derived from a modified sol–gel technique using inorganic zirconium precursor

Highly (1 0 0)-textured Pb(Zr_0.52Ti_0.48)O₃ films have been prepared on platinized silicon substrate by a modified sol–gel technique using inorganic zirconium precursor. The X-ray diffraction analysis on the crystallinity and texture evolution of sol–gel lead zirconate titanate (PZT) films revealed that the films were well crystallized to perovskite phase when annealed at 550 °C, and that highly (1 0 0) preferred orientation dominated in the PZT films after annealed at 650 °C. The (1 0 0)-oriented PZT film exhibited the remnant polarization of 26.3 μC/cm² and the coercive field of 100 kV/cm.     

Misfit strain–film thickness phase diagrams and related electromechanical properties of epitaxial ultra-thin lead zirconate titanate films

The phase stability of ultra-thin (0 0 1) oriented ferroelectric PbZr_1–xTi_xO₃ (PZT) epitaxial thin films as a function of the film composition, film thickness, and the misfit strain is analyzed using a non-linear Landau–Ginzburg–Devonshire thermodynamic model taking into account the electrical and mechanical boundary conditions. The theoretical formalism incorporates the role of the depolarization field as well as the possibility of the relaxation of in-plane strains via the formation of microstructural features such as misfit dislocations at the growth temperature and ferroelastic polydomain patterns below the paraelectric–ferroelectric phase transformation temperature. Film thickness–misfit strain phase diagrams are developed for PZT films with four different compositions (x = 1, 0.9, 0.8 and 0.7) as a function of the film thickness. The results show that the so-called rotational r-phase appears in a very narrow range of misfit strain and thickness of the film. Furthermore, the in-plane and out-of-plane dielectric permittivities ε₁₁ and ε₃₃, as well as the out-of-plane piezoelectric coefficients d₃₃ for the PZT thin films, are computed as a function of misfit strain, taking into account substrate-induced clamping. The model reveals that previously predicted ultrahigh piezoelectric coefficients due to misfit-strain-induced phase transitions are practically achievable only in an extremely narrow range of film thickness, composition and misfit strain parameter space. We also show that the dielectric and piezoelectric properties of epitaxial ferroelectric films can be tailored through strain engineering and microstructural optimization.     

Enhanced ferroelectric properties of Pb(Zr0.52Ti0.48)O3 films on Pt/TiO2/SiO2/Si(001) using ZnO buffer layer

(0 0 1)-textured Pb(Zr_0.52Ti_0.48)O₃ films have been grown on Pt/TiO₂/SiO₂/Si(0 0 1) substrates by pulsed laser deposition using Al-doped ZnO as a buffer layer and bottom electrode. The as-fabricated ferroelectric capacitors exhibit large remanent polarization and excellent fatigue and retention properties.     

Microstructural studies and electrical properties of Mg-doped SrTiO3 thin films

The structure–property relations of Mg-doped SrTiO₃ (ST) sol–gel thin films deposited on Pt/TiO₂/SiO₂/Si substrates have been investigated in order to determine the effect that Mg dopants have on the dielectric properties of SrTiO₃. It has been predicted that Mg-doped SrTiO₃ should exhibit a dielectric anomaly similar to that observed recently in Bi doped SrTiO₃ but, to date, no polar state has been reported. It has been suggested that this may relate to the low solubility of Mg on the A-site in bulk ceramics (<0.05 at.%). However, for Sr_1−xMg_xTiO₃ (SMT) (x ⩽ 0.30) films annealed at 750 °C, all Mg ions were accommodated in the perovskite lattice and for SMT films annealed at 900 °C, the solubility limit of Mg was x = 0.10, above which a Mg-rich ilmenite second phase was observed. Irrespective of the higher solid solubility limit of Mg in the ST lattice for sol–gel ST films compared to equivalent ceramics, no ferroelectric or relaxor phase transition was observed, refuting previous predictions for this dopant.     

Titanium-supported Ce-, Zr-containing oxide coatings modified by platinum or nickel and copper oxides and their catalytic activity in CO oxidation

A combination of plasma electrolytic oxidation (PEO) and impregnation techniques followed by annealing in air has been used to obtain composites Pt/nZrO₂ + pTiO₂/Ti, Pt/nZrO₂ + pTiO₂ + zCeO_x/Ti, NiO + CuO/nZrO₂ + pTiO₂/Ti, NiO + CuO/nZrO₂ + pTiO₂ + zCeO_x/Ti with different zirconium and titanium contents and ZrO₂/TiO₂ phase ratio. The composites have been investigated by means of XRD, XPS and SEM/XSA methods. According to the XPS data, the platinum content on the coating surface is ~ 0.4 at.%, whereas the XSA measurements have shown that the nickel and copper contents in coatings attain 16 and 8 at.%, respectively, depending on the initial oxide coatings composition. Nickel and copper oxides form either extended islets or solid layers (“crusts”) on the coating surface. Both the composites promoted with platinum and those with the “crust” built from nickel and copper oxides are active in CO oxidation at the temperatures above 200 °C and 300 °C, respectively.     

Structural and compositional homogeneity of InAlN epitaxial layers nearly lattice-matched to GaN

A group of InAlN films was fabricated by molecular beam epitaxy and investigated by X-ray diffraction, transmission electron microscopy and element nano-analyses. All top In_xAl_1?xN layers have compositions around lateral lattice-matching to GaN (x ≈ 0.18) and are pseudomorphic. For a growth rate of 350 nm h^?1, each InAlN film separated into two sublayers with different In/Al-ratios. Micrographs reveal sharp transitions both at the InAlN/GaN and at the InAlN/InAlN interfaces. In contrast to these separated layers, an optimized epitaxy using an AlN interlayer and a lower growth rate, 100 nm h^?1, enabled the fabrication of a single-phase In_xAl_1?xN layer on GaN, homogeneous on a nanoscopic scale.     

High-temperature ferromagnetism observed in facing-target reactive sputtered MnxTi1−xO2 films

The crystal structure of reactive sputtered Mn_xTi_1−xO₂ films turns from anatase to rutile as x increases. All the films are ferromagnetic, with a Curie temperature above 340 K. Vacuum annealing enhances the ferromagnetism of the films, but O₂ annealing weakens it, indicating that the ferromagnetism is related to the oxygen-vacancy defects created by Mn⁺² dopants at Ti⁺⁴ cations. The average room-temperature moment per Mn decreases from 0.482 μ_B at x = 0.026 to 0.078 μ_B at x = 0.375. Meanwhile, the optical band gaps value decreases linearly from 3.35 eV at x = 0 to 1.73 eV at x = 0.375, suggesting that Mn ions substitute for Ti ions uniformly and the ferromagnetism is not from magnetic Mn oxide impurities. The high-temperature ferromagnetism makes the Mn_xTi_1−xO₂ films useful for the applications in spintronic devices.     

Laves phases in the ternary systems Ti–{Pd,Pt}–Al

Formation and crystal structure of Laves phases in the systems Ti–{Pd,Pt}–Al were investigated employing XPD (X-ray powder diffraction), XSCD (X-ray single crystal diffraction) and EPMA (electron probe microanalysis) techniques. Laves phases with MgZn₂ type (space group: P6₃/mmc) and its variant with the Nb(Ir,Al)₂-type (a√3 × a√3 × c supercell of MgZn₂-type, space group: P6₃/mcm) were found in both systems. Formation of a particular structure type is dependent on temperature and composition. Laves phases with the Nb(Ir,Al)₂-type form around 25 at.% of Pd,Pt at 950 °C. The MgZn₂-type Laves phase Ti(Pt,Al)₂ was not observed at 950 °C, but it forms in as-cast alloys at a slightly lower Pt content, Ti_37.8Pt_19.0Al_43.2. In the Ti–Pd–Al system at 950 °C the MgZn₂-type phase exists at the Pd-poor side of the homogeneity region whilst the Nb(Ir,Al)₂-type phase is slightly richer in Pd. Phase relations associated with the Ti–Pt–Al Laves phase were established at 950 °C and reveal a new compound TiPtAl that derives from hexagonal ZrBeSi-type (ordered Ni₂In-type, a = 0.43925(4) nm, c = 0.54844(5); space group P6₃/mmc; R_F2 = 0.015 from single crystal data). Atom distribution in the compound shows a slight deviation from full atom order Ti(Pt_0.97Al_0.03)(Al_0.98Pt_0.02).     

Structural phase transformation and electrical properties of (0.90 – x)Pb(Mg1/3Nb2/3)O3–xPbTiO3–0.10Pb(Fe1/2Nb1/2)O3 ferroelectric ceramics near the morphotropic phase boundary

Novel solid solutions of (0.90 – x)Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃–0.10Pb(Fe_1/2Nb_1/2)O₃, where x = 0.29, 0.31, 0.33 and 0.35, were investigated from the viewpoint of structural phase transformation, dielectric, ferroelectric and piezoelectric properties. X-ray diffraction and Raman scattering measurements demonstrated that their phase structures experienced a gradual transition process from rhombohedral to tetragonal phase near the morphotropic phase boundary (MPB) region with increasing PbTiO₃ content (x). Corresponding to the structural phase transition near the MPB, large dielectric constants (ε_r) were obtained at the compositions of x = 0.31 (ε_r = 3094 at 1 kHz) and x = 0.33 (ε_r = 2927 at 1 kHz). The maximum remnant polarization (P_r = 26.5 μC cm⁻²) was obtained at the composition x = 0.31, and the electromechanical factor (k_p = 0.59) and piezoelectric coefficient (d₃₃ = 545 pC N⁻¹) were also maximized at this composition, which indicated the enhanced electrical properties near the MPB.     

Magnetic properties of nanocrystalline ferrite TixCo1+xFe2−2xO4 and CoFe2O4 composite thin films

Ti_xCo_1+xFe_2−2xO₄ (0 ≦ x ≦ 0.5) ferrite films and its composite films with CoFe₂O₄ synthesized by a sol–gel method were investigated on crystallographic and magnetic properties. Magnetization decreased with the increase of Ti content while coercive force showed a maximum at x = 0.2 and comparatively high at x = 0.5. Composite films of Ti_0.5Co_1.5FeO₄ and CoFe₂O₄ showed larger H_c and smaller grains.     

An investigation of the effect of structural order on magnetostriction and magnetic behavior of Fe–Ga alloy thin films

This paper reports results from a comprehensive study of Fe–Ga films fabricated over a wide range of growth conditions. Polycrystalline Fe_100?xGa_x films (14 ? x ? 32) were deposited (using three different combinations of growth parameters) on Si(1 0 0) using a co-sputtering and evaporation technique. The growth parameters (sputter power, Ga evaporation rate and chamber pressure) were used primarily to control the Fe:Ga ratio in the films. X-ray diffraction showed that all films had 〈1 1 0〉 crystallographic texture normal to the film plane. The lattice parameter increased with % Ga up to x = 22 and was independent of growth parameters. Conversion electron Mössbauer spectroscopy studies showed a predominance of the disordered A2 phase in all films. It appears that the use of vacuum deposition with appropriate parameters can effectively suppress the D0₃ ordered phase. Systematic studies of the effective magnetostriction constant as a function of composition support this conclusion. It was found that films of high effective saturation magnetostriction constant and low stress could be fabricated using low Ar pressure, irrespective of sputter power or evaporation rate, giving properties useful for application in microelectromechanical systems.     

Usefulness of aqueous micellar media for electrosynthesis of poly(N-phenylpyrrole). Characterization and optical properties

Poly-N-phenyl-pyrrole [poly(N-PhPy)] was electrosynthesized by anodic oxidation of N-PhPy on Pt electrode in acid aqueous micellar medium (0.1 M sodium dodecyl sulfate (SDS) + 1.93 M HClO₄ in 84/16 water/butanol v/v), using cyclic voltammetry (CV), chronoamperometry and chronopotentiometry. Electroactive poly(N-PhPy) films were formed upon scanning the potential (E) between 0.0 and 1.4 V/SCE, under controlled potential (E = 0.9–1.3 V/SCE) or controlled current density (J = 0.125–2.0 mA/cm²). The poly-NPhPy films were characterized by CV, MALDI-TOF mass spectrometry, FT-IR and X-ray photoelectron spectra (XPS), and their morphology was studied by scanning electron microscopy (SEM). Their optical properties, including electronic absorption and fluorescence spectra, were also investigated. A multiple-step mechanism for the poly(N-PhPy) films formation in micellar medium, based on the MALDI-TOF, FT-IR and XPS results, was proposed.     

Dislocation interaction of layers in the Ge/Ge-seed/GexSi1−x/Si(0 0 1) (x ∼ 0.3–0.5) system: Trapping of misfit dislocations on the Ge-seed/GeSi interface

High-resolution electron microscopy has been applied to study the dislocation redistribution between Ge and GeSi layers at the atomic scale. Ge_0.3Si_0.7 (30 nm in thickness) and Ge_0.5Si_0.5 (10 nm) buffer layers buried between the Si(0 0 1) substrate and the plastically relaxed Ge layer 0.5 μm thick remain in a metastable (stressed) state during the growth of Ge/Ge-seed/Ge_xSi_1?x/Si(0 0 1) (x ～ 0.3–0.5) heterostructures, though the buffer layer thickness is several times greater than the critical value for insertion of misfit dislocations (MDs). An ordered grid of edge MDs is observed only on the Ge/GeSi interface; the mean distance between the MDs is ～10 nm (which is close to the equilibrium value for the non-stressed Ge/Si system). After 30 min of annealing at 700 °С, the Ge_0.3Si_0.7 buffer layer still remains in a metastable state, and the edge MDs are located only on the Ge/GeSi interface with the same dislocation spacing of ～10 nm. At the same time, approximately one-half of MDs in the structure with the Ge_0.5Si_0.5 buffer layer passes through the Ge/GeSi interface to the GeSi/Si(0 0 1) interface, and the buffer layer plastically relaxes by almost 100%. An assumption is put forward that there exists a barrier for the MD transition from the Ge layer to the GeSi layer, which results in MD trapping on this interface. The magnitude of this barrier depends on the difference in the compositions of the main Ge (x = 1) film and the Ge_xSi_1?x buffer layer, and increases with increasing this difference.     

Isothermal section of the Er–Fe–Al ternary system at 800 °C

Physico-chemical analysis techniques, including X-ray diffraction and Scanning Electron Microscope–Energy Dispersive X-ray Spectroscopy, were employed to construct the isothermal section of the Er–Fe–Al system at 800 °C. At this temperature, the phase diagram is characterized by the formation of five intermediate phases, ErFe_12?xAl_x with 5 ≤ x ≤ 8 (ThMn₁₂-type), ErFe_1+xAl_1?x with ?0.2 ≤ x ≤ 0.75 (MgZn₂-type), ErFe_3?xAl_x with 0.5 < x ≤ 1 (DyFe₂Al-type), Er₂Fe_17?xAl_x with 4.74 ≤ x ≤ 5.7 (TbCu₇-type) and Er₂Fe_17?xAl_x with 5.7 < x ≤ 9.5 (Th₂Zn₁₇-type), seven extensions of binaries into the ternary system; ErFe_xAl_3?x with x < 0.5 (Au₃Cu-type), ErFe_xAl_2?x with x ≤ 0.68 (MgCu₂-type), Er₂Fe_xAl_1?x with x ≤ 0.25 (Co₂Si-type), ErFe_2?xAl_x with x ≤ 0.5 (MgCu₂-type), ErFe_3?xAl_x with x ≤ 0.5 (Be₃Nb-type), Er₆Fe_23?xAl_x with x ≤ 8 (Th₆Mn₂₃-type), and Er₂Fe_17?xAl_x with x ≤ 4.75 (Th₂Ni₁₇-type) and one intermetallic compound; the ErFe₂Al₁₀ (YbFe₂Al₁₀-type).     

Correlation between microhardness and electronic charge density of hafnium hydrides

Quantitative Vickers microhardnesses for α + δ′-, δ′-, δ-, δ + ?- and ?-phase hafnium hydrides (HfH_x; 1.46 ≤ x ≤ 2.02) and deuterides (HfD_x; 1.55 ≤ x ≤ 1.94) at room temperature have been measured using a Vickers hardness tester. The Vickers microhardnesses of the HfH_x and HfD_x gradually decreased with an increase of the hydrogen concentration, and those for 1.46 ≤ x ≤ 1.70 were higher than that of α-phase metallic Hf. It was revealed by a first-principles calculation as well as an X-ray photoelectron spectroscopy (XPS) measurement that the hydrogen concentration dependence of the microhardnesses for HfH_x and HfD_x was ascribed mainly in terms of its influence on charge transfer from Hf 5d to H 1s and reduction of cohesive energy.     

Structural and mechanical properties of Cr–Al–O–N thin films grown by cathodic arc deposition

Coatings of (Cr_xAl_1?x)_δ(O_1?yN_y)_ξ with 0.33 ? x ? 0.96, 0 ? y ? 1 and 0.63 ? δ/ξ ? 1.30 were deposited using cathodic arc evaporation in N₂/O₂ reactive gas mixtures on 50 V negatively biased WC–10 wt.% Co substrates from different Cr and Al alloys with three different Cr/Al compositional ratios. For N₂ < 63% of the total gas, ternary (Cr,Al)₂O₃ films containing <1 at.% of N forms; as determined by elastic recoil detection analysis. Increasing the N₂ fraction to 75% and above results in formation of quaternary oxynitride films. Phase analyses of the films by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy show the predominance of cubic Cr–Al–N and cubic-(Cr,Al)₂O₃ solid solutions and secondary hexagonal α-(Cr,Al)₂O₃ solid solution. High Cr and Al contents result in films with higher roughness, while high N and O contents result in smoother surfaces. Nanoindentation hardness measurements showed that Al-rich oxide or nitride films have hardness values of 24–28 GPa, whereas the oxynitride films have a hardness of ～30 GPa, regardless of the Cr and Al contents. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.