Enhanced ferroelectric properties of Pb(Zr0.80Ti0.20)O3/PbO thin films prepared by radio frequency magnetron sputtering

The Pb(Zr_0.80Ti_0.20)O₃ (PZT) thin films with and without a PbO buffer layer were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by radio frequency (rf) magnetron sputtering method. The PbO buffer layer improves the microstructure and electrical properties of the PZT thin films. High phase purity and good microstructure of the PZT thin films with a PbO buffer layer were obtained. The effect of the PbO buffer layer on the ferroelectric properties of the PZT thin films was also investigated. The PZT thin films with a PbO buffer layer possess better ferroelectric properties with higher remnant polarization (P_r = 25.6 μC/cm²), and lower coercive field (E_c = 60.5 kV/cm) than that of the films without a PbO buffer layer (P_r = 9.4 μC/cm², E_c = 101.3 kV/cm). Enhanced ferroelectric properties of the PZT thin films with a PbO buffer layer is attributed to high phase purity and good microstructure.     

Characterization of lead zirconate titanate thin film deposition onto Pt/Ti/SiO2/Si substrates

Lead zirconate titanate, (Pb(Zr_0.52Ti_0.48)O₃PZT) thin films were deposited onto a Pt/Ti/SiO_2/Si substrate using radio frequency (r.f.) planar magnetron sputtering in this study. The deposited PZT thin films were almost amorphous before the annealing processes and developed a perovskite structure after the annealing process. If the annealing temperature was too low or annealing time too short, pyrochlore would form. However, if the annealing temperature was too high or annealing time too long, the thin film structure would degrade due to the volatilization of PbO. The significant finding in this experiment is that high quality perovskite PZT thin films on Pt/Ti/SiO_2/Si substrates can be obtained by adjusting the annealing temperature to a range of 650 °C to 850 °C and annealing time to a range from 5 to 80 min. In this experiment, the optimal annealing condition was an annealing temperature of 650 °C and time of 20 min. The properties of PZT thin film annealed at 650 °C for 20 min were dielectric constant _r = 869 free dielectric constant ^T ₃₃ = 893 piezoelectric constant d₃₃ = 2.03p m V^-1 piezoelectric constant g₃₃ = 2.57 x 10^-4 V m N^-1, remanent polarization P₁ = 112.5 nC cm^-2 and coercive field E_c= 0.061 kV cm^-1.     

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.     

Electrical properties of non c-axis oriented SrBi2(Ta0.95V0.05)2O9 thin films

Pulsed laser deposition technique was used to grow off c-axis oriented SrBi₂(Ta_0.95V_0.05)₂O₉ (SBTV) ferroelectric thin films. X-ray diffraction studies revealed the c-axis suppression in the films grown at lower substrate temperature (350°C) followed by annealing at higher temperatures (650°C). In-plane lattice parameters of the films were decreased with increase in annealing temperature. SBTV films annealed at 750°C exhibited enhanced ferroelectric properties with remanent polarization (2P _r) of 31.5 C/cm² and coercive field (E _c) of 157 kV/cm. The dielectric permmitivity of the films increased with increase in annealing temperature and it was attributed to the grain size dependence. The films annealed at 750°C showed maximum value of dielectric permittivity 172 with a tangential loss of 0.1, at 100 kHz. Higher value of dissipation factor at lower annealing temperature is explained in terms of space charge accumulation at grain boundaries. The leakage current densities of the films follow ohmic behavior at low field regime and space charge limited current dominates at higher fields.     

Synthesis of (Pb,La) (Zr,Ti)O3 films using a diol based sol–gel route

Morphotropic phase boundary compositions of lead zirconate titanate (PZT) modified with 2, 5 and 10 mol% lanthanum (PLZT) have been prepared using a diol based sol–gel route. Thin films of these PLZT compositions were fabricated on platinized silicon substrates by a spin coating technique. The effects of firing temperature and lanthanum modifications were investigated with regard to phase development, microstructure, and ferroelectric and dielectric characteristics. A strong 1 1 1 orientation developed as the amount of lanthanum doping increased. The results indicate that the values of remanent polarization, P _r, and dielectric constant, _r, decrease, relative to unmodified PZT, for films modified with 2 and 5 mol% lanthanum. The 5 mol% La films for example had a P _r of 14 C cm^–2 and an _r value of 700 compared to 31 C cm^–2 and 1480 for undoped PZT films. At these La concentrations there was also an improvement in the leakage current density by two orders of magnitude compared with unmodified PZT. The 10 mol% La sample did not exhibit any switchable polarization behaviour.     

Annealing effects on the structural and optical characteristics of electron beam deposited Ge-Se-Bi thin films

Measurements of absorbance and transmittance in Ge₂₀Se_80-xBi_x (0 x 10 at %) chalcogenide thin films in the visible range at room temperature were carried out. The dependence of the optical absorption on the photon energy is described by the relation hv=B(hv-E₀)². It was found that the optical energy gap E₀ decreases gradually from 1.93 to 1.205 eV with increasing Bi content up to 10 at %. The rate of the change decreases with increasing Bi content. The composition dependence of the optical energy gap is discussed on the basis of the concentration of covalent bonds formed in the chalcogenide film. The decrease of optical energy gap with increasing Bi content is related to the increase of Bi–Se bonds and the decrease of Se-Se bonds. The effect of thermal annealing for different periods of time on the behavior of optical absorption of the as-deposited films was investigated. The optical gap increases with increasing annealing time. The rate of change decreases with increasing annealing time, then E₀ reaches a steady state. The increase in the values of the optical gap of the amorphous films with heat treatment is interpreted in terms of the density of states model. The structure of the as-prepared and thermally annealed films were investigated using transmission electron microscopy, energy dispersive analysis and X-ray diffraction. It was confirmed that the as-prepared films were in the amorphous state. Phase separation was observed after thermal annealing. The separated crystalline phases were identified.     

Direct current electrical conduction in lead tungsten phosphate glasses

Measurements have been made on d.c. electrical conductivity of semiconducting lead tungsten phosphate glasses (X mol% WO₃–(60–x) mol% PbO–40 mol% P₂O₅;x= 10, 20, 30, 40, 50 and 60) of six different compositions over a temperature range of 240 to 500 K. It is shown that the conduction can be described by a small polaron hopping model. When the WO₃ content is 30 mol% the d.c. conductivity _dc decreases and the activation energyW increases with increasing WO₃ content and the glass samples exhibit predominant ionic conduction, however, when the WO₃ content is > 30 mol%, _dc increases andW decreases with the increase of tungsten ion concentration and the glass samples exhibit electronic conduction. The electronic conduction in these glasses havingx > 30 mol% seems to be adiabatic. Greaves variable range hopping has been found to be valid. The value of the electron wavefunction decay constant a is of the order of 16 nm^–1. A minimum in the d.c. conductivity has been observed when the PbO concentration is 30 mol%.     

Preparation and characterization of preferred oriented PZT films on amorphous substrates

The (001) preferred orientation of Nb-doped Pb(Zr_0.52Ti_0.48) O₃ (PZT) thin films was successfully realized on amorphous glass substrate with LaNiO₃(LNO) as electrode by rf-sputtering method. It was found that the LNO film greatly promotes formation of the PZT film with pervoskite phase on amorphous substrate and the preferred orientation of the PZT film depends strongly on the process of preparation. The experimental results show that the dielectric constant and loss of the PZT films with the (001) preferred orientation are 1308 and 0.042, respectively, at 1 kHz, 0.05 V. The remanent polarization (P_r), saturation polarization (P_s) and coercive field (E_c) are 34.5, 43 C/cm² and 105 kV/cm, respectively. The PZT films also show a 33 kV/cm internal bias field due to its (001) preferred orientation. The piezoelectric coefficient d₃₃ of the PZT film without the poled treatment is about 15 pC/N due to its (001) preferred orientation. The effect of the foreign stress on the piezoelectric voltage response of the PZT/LNO/glass was investigated. The results make us consider using the PZT film as an artificial skin to realize the self-diagnosis of amorphous materials under the action of stress.     

Millimetre-sized hollow spheres of lead zirconate titanate by a sol-gel method

Hollow spheres of lead zirconate titanate (PZT) [chemical formula Pb(Zr_0.52Ti_0.48)O₃)], with outer diameter of 1–2 mm and a wall thickness of about 100 m, were fabricated by gellation of a PZT sol inside solid polymer spheres and then burning the polymer out. Monomodally sized polyacrylamide spheres, with diameter 1.40–1.90 mm, were soaked in a PZT sol, prepared by dissolving Pb(NO₃)₂, zirconiumn-butoxide and titanium isopropoxide inN, N-dimethylformamide. The absorbed sol was then gelled beneath the surface of the polymer sphere by the action of NH₃. Upon calcination of the spheres at 850 °C for 4 h in air, hollow spheres of pure PZT perovskite phase (as identified by X-ray diffraction patterns) were obtained. The density of the hollow spheres was 1.13gcm^–3, while that of the wall of the spheres was 3.10g cm^–3. The scanning electron microscopic examination of the broken spheres showed that the inner surface of the spheres contained rib-like structures, which provided strength to the hollow spheres. The planar coupling factor,k _p, of six hollow spheres, placed at a close-packed arrangement in a plane, was 0.22, indicating the possibility of fabrication of low-density transducer arrays.     

Optical constants and electrical conductivity of Ge20Se60Sb20 thin films

Optical absorption and electrical resistivity of amorphous Ge₂₀Se₆₀Sb₂₀ films are investigated as a function of the thermal annealing. The dependence of the optical absorption coefficient on the photon energy is ascribed by the relation (h) = B(h–E_o)². Increasing the annealing temperature from 423 K to 553 K, decreases the optical gap of the film from 1.25 eV to 0.78 eV. The effect of annealing temperature on high frequency dielectric constant () and carrier concentration (N) was also studied. As a result of annealing the film at 533 K, the electrical resistivity and activation energy for conduction decreased from 5.7 × 10⁷ to 2.9 × 10² ·cm and from 0.94 to 0.34 eV, respectively. The crystalline structures resulting from heat treatment at different elevated temperatures have been studied by X-ray Diffraction (XRD). The optical and electrical changes were attributed to the amorphous-crystalline transformations in the chalcogenide films.     

Electrical characteristics of the MOD-derived SrBi2xTa2O9 and SrBi2.4(Ta,Nb)2O9 thin films

Ferroelectric and leakage current characteristics of the MOD-derived SrBi_2xTa₂O₉ (0.8 x 1.6) and SrBi_2.4(Ta_1-yNb_y)₂ O₉ (0 y 1) thin films were investigated. The SBT and SBTN films were fully crystallized to Bi-layered perovskite structure by annealing at 800°C for 1 hour in oxygen atmosphere. The ferroelectric characteristics of the SBT films were optimized at the Bi/Ta mole ratio x of 1.2. The leakage current density of the Bi-excess SBT films decreased remarkably by the post-metallization annealing at 800°C for 10 minutes in oxygen ambient. The ferroelectric characteristics of the SBTN films were optimized with the SBN content y of 0.25. The SrBi_2.4(Ta_0.75Nb_0.25)₂ O₉ film exhibited 2P_r and E_c of 19.04 C/cm² and 24.94 kV/cm at ±5 V, which were superior to 2P_r of 11.3 C/cm² and E_c of 39.6 kV/cm obtained for the SrBi_2.4Ta₂O₉ film after the post-metallization annealing. The MOD-derived SrBi_2.4(Ta_0.75Nb_0.25)₂O₉ film did not exhibit the polarization fatigue after 10¹¹ switching cycles at ±5 V.     

Formation and characteristics of lead lanthanum zirconium titanate thin films formed by using the r.f. sputtering method

PLZT (lead lanthanum zirconium titanate) thin films were prepared by using the r.f. magnetron sputtering method and post-annealing for crystallization at 650 C. The films which were annealed at 650 C for 10 min consisted of a metastable phase and a stable phase. However, another film which was annealed at 650 C for 20 min had only stable perfect perovskite phase. The stability of the post-annealed thin film and substrate interfaces was observed by using scanning electron microscopy. The longer the annealing time, the more unstable were the interfaces. By analysing the EDX data, the composition difference between the sputtering target and thin films, and the composition variation between as-deposited and post-annealed PLZT were studied. The films annealed at 650 C for 20 min showed good ferroelectric and electrical properties with a remanent polarization (P _r) of 11.5 C cm^–2, and a coercive field (E _c) of 164 kV cm^–1.     

Parallel-plate resonator of variable spacer thickness for accurate measurements of surface impedance of high-Tc superconductive films

Measurements of microwave surface impedance of high-T _c films at gigahertz frequencies and nitrogen temperature are performed. A simple technique employing a parallel-plate resonator with liquid nitrogen as a dielectric spaces is suggested. The use of a precise mechanical device provides smooth changing of distance between films from 200m down to zero. Coupling to the resonator is accomplished by means of two small antennas-half-wave vibrators for frequency 10 GHz. The method for determining resistivity and magnetic field penetration depth was based on the analysis of spacer thickness dependences of the resonator quality factor and frequency. YBa₂Cu₃O₇ films produced by a laser deposition technique on CaNdAlO₄ substrates withT _c =91 K andj _c =10⁷ A/cm² and on NdGaO₃ substrates withT _c =91 K andj _c =10⁶ A/cm² are examined, and the valuesR _s =0.6 m,=348 nm atf=8.97 GHz andR _s =0.5 m,=250 nm atf=10.12 GHz, respectively, are obtained at 77 K.     

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.     

Effect of composition on ferroelectric properties of sol-gel derived lead bismuth titanate (PbBi4Ti4O15) thin films

Bismuth layer-structured ferroelectric PbBi₄Ti₄O₁₅(PBT) thin films were fabricated on Pt/Ti/SiO₂/Si substrates by sol-gel spin coating and the effect of lead and bismuth concentration on phase transition, microstructure and ferroelectric property was investigated. Especially, the effect of non-stoichiometric compositions, that is, deficient concentration of Pb and excess concentration of Bi with respect to the stoichiometric composition, was examined. With an increase of lead and bismuth concentration, the pyrochlore phase was suppressed and PBT phase was developed. Large increases of 2P _r and 2E _c were also observed as lead and bismuth concentration increased. An improved ferroelectric property could be obtained by inserting a Bi-rich buffer layer between Pt electrode and Pb-rich PBT film. The PBT thin films with Bi-rich buffer layer showed homogeneous grain size distribution, good fatigue endurance up to 1 × 10⁹ switching cycles, low relative permittivity of 270 and sufficient 2P _r values of 15.7 C/cm².     

Ferroelectric Lead Zirconate Titanate Films Prepared by Spray Pyrolysis of Carboxylate Solutions

Ferroelectric PbTi_0.6Zr_0.4O₃films 0.5–1.5 m in thickness were produced on platinum substrates by spray pyrolysis of carboxylate solutions. The optimized compositions of the precursor solutions, containing methacrylic acid and ethylene glycol, are stable under normal conditions, allow the annealing temperature to be reduced, and lead to higher quality film surfaces and large grains. The film exhibit the following electrical properties: T _C= 360–460°C, _max= 1750 at T _C, tan = 0.02–0.1 at 1 kHz and room temperature, P _{s max} = 18 C/cm², P _{r max} = 15 C/cm²at 50 Hz, and E _c= 42–120 kV/cm.     

Transport properties of CdGa2Se4 thin films

The d.c. conductivity was determined for CdGa₂Se₄ thin films in the temperature range 300–625 K for as-deposited and heat-treated films. The conductivity at room temperature of films of thickness 326 nm prepared at a temperature of 573 K was found to be 10^–12 ( cm)^–1. The dependence of the electrical conductivity on the annealing temperature in a vacuum of 1 Pa for a thin film of thickness 140 nm, shows that the electrical conductivity increases with increasing annealing temperature. However, the activation energies E and E decrease with increasing annealing temperature. The data of these annealed films are in agreement with the Meyer–Neldel rule. The thermoelectric power measurements indicate p-type conduction in the as-deposited films as well as for the heat-treated films. The p-type conduction is due to the cadmium deficiency as indicated by EDX. The difference between the value of the activation energy calculated from the thermoelectric power E _S and that obtained from the conductivity E indicates the presence of long-range potential fluctuations.     

Structural and electrical properties of cadmium-sulpho-selenide solid solutions

Complete solid solutions of CdS _x Se_1–x (0x1) were synthesized by vacuum fusion of stoichiometric proportions of CdS and CdSe. X-ray diffraction data revealed that they possess the hexagonal wurtzite structure. The unit cell lattice constants vary linearly with the composition parameter,x, following Vegard's law.Thin films of CdS _x Se_1–x (0x1) solid solutions could be deposited onto glass substrates by thermal evaporation of the bulk material in 10^–4 Pa vacuum. Structural investigation showed that the films are polycrystalline with predominant appearance of the (002) reflecting plane. On annealing at 250°C in 10^–2 Pa vacuum atmosphere, aggregation and rearrangement of the as-deposited tiny crystallite occurred, preserving the same crystal structure.The dark electrical resistivity of the films is independent on the film thickness, but it varies appreciably with the composition parameter,x, showing a minimum resistivity of 0.02 cm atx=0.55. The temperature dependence of the resistivity follows the semiconducting behaviour with an extrinsic and an intrinsic conduction below and above 70°C, respectively. The determined activation energies 0.2 eV and 0.8 eV, respectively, correspond to shallow and deep trap levels, respectively.     

The influence of annealing processes on the structural, compositional and electro-optical properties of CuIn0.75Ga0.25Se2 thin films

Crystalline defects, such as the density of voids, grain boundaries and dislocations, in Cu(In,Ga) Se₂ absorber layers depend on the fabrication conditions and determine to a large extent the efficiency of photovoltaic devices. The material properties, however, can be improved significantly by using post-deposition processes. In this paper, the effects of post-deposition heat treatments on properties of CuIn_0.75Ga_0.25Se₂ (CIGS) thin films are investigated. Selected flash evaporated samples were subsequently processed under several sets of conditions, including vacuum, selenium, inert (argon) and forming gas (a 9:1 mixture of N₂:H₂) ambients, at different temperature and times. Structural, compositional and electro-optical properties of both as-deposited and annealed films were studied using a variety of analytical techniques. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies of the films showed a columnar grain structure with strong < 112 > preferred orientation, which after heat treatments relaxed to give a chalcopyrite structure. Raman analysis showed that the annealing process reduced the full-wave half-maximum (FWHM) value from 20 to 10 cm^–1 indicating a change in both film composition and microstructure. In addition, X-ray fluorescence (XRF) and Rutherford backscattering spectroscopy (RBS) revealed that the composition was approaching that of the polycrystalline starting material. Both n- and p-type conductivities were observed with resistivity values in the range 10^–1 to 10⁶ cm. Annealing in selenium atmosphere altered the n-type conductivity to p-type. To confirm improvements in optical properties of annealed films, photoacoustic spectroscopy (PAS) was employed.     

Ferroelectric properties of Mn-Doped Bi3.15Nd0.85Ti3O12 thin films prepared under different annealing conditions

Mn-doped Bi_3.15Nd_0.85Ti₃O₁₂ (BNTM) thin films were fabricated on Pt/Ti/SiO₂/Si(100) substrates by a chemical solution deposition technique and annealed at different temperatures from 650 to 800 °C. The structures of the films were analyzed using X-ray diffraction, which showed that the BNTM films exhibit polycrystalline structures and random orientations. The surface morphologies of the samples were investigated using scanning electron microscopy. The average grain size of the films increases with increasing annealing temperature. Electrical properties such as remanent polarization (2P_r) are quite dependent on the annealing temperature of BNTM films. It is found that the film annealed at 750 °C exhibits excellent ferroelectricity with a remanent polarization of 2P_r = 89.3 μC/cm² and a coercive field of E_c = 99.2 kV/cm respectively.