Influence of Nb2O5 doped amount on the property of BCTZ lead-free piezoelectric ceramics doped with Li2CO3

Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ (BCTZ) lead-free piezoelectric ceramics doped with Nb₂O₅ (0.1, 0.3, 0.5, 0.7, 0.9 wt%) and Li₂CO₃ (0.6 wt%) were prepared by conventional solid-state reaction method. Influence of Nb₂O₅ doping amount on the piezoelectric property, dielectric property, phase composition and microstructure of prepared BCTZ lead-free piezoelectric ceramics doped with Li₂CO₃ were investigated by X-ray diffraction and scanning electron microscopy and other analytical methods. The results showed that the sintered temperature decreased greatly when the BCTZ lead-free piezoelectric ceramics were co-doped with Nb₂O₅ and Li₂CO₃; a pure perovskite structure of BCTZ lead-free piezoelectric ceramics co-doped with Nb₂O₅ and Li₂CO₃ sintered at 1,020 °C could be also obtained. The grain size decreased when Nb₂O₅ doping amount increased. The piezoelectric constant (d₃₃), the planar electromechanical coupling factor (k_p), the relative dielectric constant (ε_r) of BCTZ ceramics doped with Li₂CO₃ increased firstly and then decreased, the dielectric loss (tanδ) decreased firstly and then increased when Nb₂O₅ doping amount increased, indicating that Nb₂O₅ was “soft” additive. When Nb₂O₅ doping amount (z) was 0.7 wt% and Li₂CO₃ doping amount was 0.6 wt%, the BCTZ ceramics sintered at 1,020 °C possessed the best piezoelectric property and dielectric property, which d₃₃ was 238 pC/N, k_p was 29.33 %, ε_r was 4,691, tanδ was 2.07 %.     

New applications of photostrictive ferroics

 Photostriction in ferroelectrics arises from a superposition of photovoltaic and inverse piezoelectric effects. (Pb,La)(Zr,Ti)O₃ ceramics doped with WO₃ exhibit large photostriction under irradiation of near-ultraviolet light, and are applicable to remote control actuators and photoacoustic devices. Using a bimorph configuration, a photo-driven relay and a micro walking device have been developed, which are designed to start moving as a result from the irradiation, having neither electric lead wires nor electric circuits. The mechanical resonance of the bimorph was also induced by an intermittent illumination of purple-color light; this verified the feasibility of applying photostriction for ”photophone” applications. Received: 10 September 1997/Accepted: 9 October 1997     

Dielectric property of Ba0.6Sr0.4TiO3–Mg0.9Zn0.1O ceramic with additives of Sm2O3 and Ta2O5

Influence of Sm₂O₃ and Ta₂O₅ additions on the dielectric property of Ba_0.6Sr_0.4TiO₃–Mg_0.9Zn_0.1O (BST–MZO) ceramic composite was investigated. The XRD results indicate that the main phases in the Sm₂O₃ and Ta₂O₅ doped samples are BST and MZO. Loss tangent of BST–MZO ceramic becomes higher with additive of Sm₂O₃. Optimum doping amount of Ta₂O₅ can reduce loss tangent of BST–MZO ceramic which can also ensure the moderate dielectric constant and usable tunability. When the amount of Ta₂O₅ is 1.0 wt%, the dielectric constant, loss tangent and tunability are 84.85, 0.0005 (at 1 MHZ) and 15% (under electric field 7 kv/mm), respectively. At microwave frequency (4.025 GHz), the dielectric constant decreases to 81.03 while loss tangent increases to 0.0049. The ceramic with additive of 1.0 wt% Ta₂O₅ has the optimal FOM value (about 261) and should be a promising candidate for phase shifter application.     

Electrical properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics modified with WO3

Ferroelectrics 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) + x mol% WO₃ (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO₃-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃+2 mol% WO₃. Dielectric peak temperature decreased with WO₃ doping, indicating that W⁶⁺ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of K_max. Both piezoelectric constant (d₃₃) and electromechanical coupling factors (k_p) were enhanced by doping 0.1 mol% WO₃, which results from the introduction of “soft” characteristics into PMN-PT, while further WO₃ addition was detrimental. We consider that the two factors, introduction of “soft” characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO₃.     

Substitution du tungstene par le tantale dans les bronzes de tungstene NaxTayW1−yO3

In order to study the modification of the transport properties of Na_xWO₃ by substitution in the WO₃ sublattice, single crystals of tantalum-substituted tungsten bronzes of formula Na_xTa_yW_1?yO₃ have been grown by electrolytic reduction of fused Na₂WO₄WO₃Ta₂O₅ mixtures. The lattice constant of their cubic perovskite like structure increases with Ta content. Electric conductivity measurements on Na_xTa_yW_1?yO₃ single crystals characterize a metal-non metal transition when x-y, i.e. the number of d electrons, decreases. This transition seems to be of Anderson type.     

Reactive DC sputter-deposited tantalum oxide thin film for all-solid-state switchable mirror

We have developed an all-solid-state switchable mirror of Mg₄Ni/Pd/Ta₂O₅/WO₃/ITO on glass. Each material of Mg₄Ni, Pd, and Ta₂O₅ in the device acts as an optical switching, a proton injector and a solid electrolyte, respectively. The initial state of the device is a reflective state as a mirror and the state changes to a transparent one by applying voltage. In this work, solid electrolyte of Ta₂O₅ thin film was deposited on the WO₃/ITO/glass substrate by reactive DC magnetron sputtering with Ar/O₂ mixture gases. The effect of Ar/O₂ ratio on the electrochemical property of Ta₂O₅ thin film and the optical switching property of the device were investigated. The film deposited at Ar/O₂ of 4.7 had better electrochemical property than that of other films. The transmittance at a wavelength of 670 nm of the device using Ta₂O₅ thin film deposited at Ar/O₂ of 4.7 was reached from the reflective state of 0.1% to the transparent state of 44% less than 15 s by applying voltage of 5 V. The device showed a stable durability of up to 1000 switching cycles.     

Effect of doping and substrate temperature on the structural and optical properties of reactive pulsed laser ablated tin oxide doped tantalum oxide thin films

5% SnO₂ doped tantalum oxide (Ta₂O₅) films are deposited on quartz substrates at different substrate temperatures of 300 K, 773 K, 873 K and 973 K using pulsed laser deposition in an oxygen ambient of 0.002 mbar. Undoped Ta₂O₅ films are also deposited on quartz substrates kept at substrate temperature 973 K under the same oxygen ambient using PLD. The films are characterized using GIXRD, AFM, FTIR, micro-Raman and UV-visible spectroscopy. Undoped films show an amorphous nature even at a substrate temperature of 973 K, whereas, SnO₂ doped films show crystalline nature even for deposition at 300 K. As far as our knowledge goes, this is the first report of crystalline Ta₂O₅ films deposited at room temperature. The average size of the crystallites calculated using the Debye-Scherrer formula, shows that the size of the crystallite decreases with increase in substrate temperature. FTIR and micro-Raman spectroscopic analysis reveals the presence of Ta-O-Ta, O-Ta and O-Ta-O vibrational bands in the films. Raman analysis indicates that the addition of SnO₂ suppresses the bond formation and changes the magnitude of bonds in Ta₂O₅. AFM patterns reveal the formation of Ta₂O₅ nanorods of diameter about 100 nm for the doped film deposited at 973 K. Optical transmittance of the films is found to be sensitive to substrate temperature as well as to the presence of SnO₂. A blue shift in the band-gap of the doped films is observed. The decrease of band-gap with decrease of particle size observed for SnO₂ doped films can be due to a band-bending effect. The transmittance of the films is found to depend on SnO₂ doping and substrate temperature.     

Microstructure and Optical Properties of Tantalum Modified TiO<Subscript>2</Subscript> Thin Films Prepared by the Sol–Gel Process

Tantalum doped TiO₂ thin films ((TiO₂)_1−x (Ta₂O₅) _x , x=0, 0.1%, 0.3%, 0.5%, 0.8%) were prepared on ITO-coated substrates by means of the sol–gel method and spin coating technology followed by rapid thermal annealing treatment (RTA). The effects of various processing parameters, including Ta content (x=0–0.8%) and annealing temperature, on the growth and properties of thin films were investigated. Structural characteristics by X-ray diffraction analysis indicated that the doping of Ta₂O₅ in the TiO₂ without change the anatase structure of TiO₂ thin films. The optical transmittance of (TiO₂)_1−x (Ta₂O₅) _x thin films decrease from 50% down to 20% with increasing the Ta₂O₅ concentrations from x=0.00 to x=0.8%. The absorption coefficient shows energy gap were decreased with increasing Ta₂O₅ content from 2.932 eV for x=0.00 to 2.717 eV for x=0.8%. Doping TiO₂ with Ta₂O₅ can lower its band gap and shift its optical response to the visible region.     

Optical and electrochemical properties of all-solid-state transmittance-type electrochromic devices

Using a vacuum dry process, we constructed an all-solid-state transmittance-type electrochromic (EC) device consisting of five thin layers: ITO/IrO_x/Ta₂O₅/WO₃/ITO. We measured the optical and electrochemical properties of the EC device. By using Ta₂O₅ film as a proton conducting solid electrolyte, the device exhibited a fast response speed of 0.2 s and stable coloration characteristics. With an AC impedance method, we determined the properties of the device under varying temperature and environmental conditions. In the solid electrolyte (Ta₂O₅), the ion resistance controlled the response speed; the ionic conductivity and activation energy were 3 × 10^− 6 S/cm and 0.31 eV, respectively.     

Characterization and sintering of a porous glass-ceramic in the system Na2O-B2O3-Ta2O5

Substitution of SiO₂ in the ternary sodium borosilicate system with Ta₂O₅ was found to produce glasses, which after heat treatment separated into immiscible microphases, one of which was water soluble. The structure of the leached material after heat treatment was a well developed low temperature form of Ta₂O₅. After firing at temperatures between 1100 and 1550°C X-ray diffraction analysis showed the presence of low and high temperature forms of Ta₂O₅ and of orthorhombic Na₂Ta₅O₂₁. The high solubility of up to 40 wt% Ta₂O₅ in the sodium-borate matrix resulting in clear glasses is of practical interest. The specific surface areas of the leached materials ranged between 5.54 and 35.57 m²g⁻¹ while in an additionally Al₂O₃ doped material the value of 307 m²g⁻¹ was measured. Mean pore radii of interconnected pores were calculated to be between 18.63 to 41.12 nm in the Ta₂O₅-rich materials while the additional Al₂O₃ doping decreased the value to 2.71 nm. A sintering temperature between 1500 and 1550°C is estimated from void volume measurements after a series of firing steps at temperatures between 1100 and 1550°C were undertaken.     

Study of Semimagnetic Mn-Doped WO<Subscript>3</Subscript> Nanoparticles Synthesised by Precipitation Method: Hydrogenation Creates a Promising DMS

Abstract Tungsten oxide (WO₃) nanoparticles doped with different amounts of manganese ions (W_1?x Mn _x O₃, where x =?0.011, 0.022 and 0.044) were synthesised by hydraulic acid-assisted precipitation, followed by thermal calcinations. The powders were characterised by X-ray fluorescence (XRF), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and magnetic measurements. The monoclinic structure at room temperature (～293 K) found for un-doped WO₃ was preserved even with Mn doping. However, doping with Mn ions caused decease in unit-cell volume and slight increase in crystallite size (CS) of host WO₃. The hydrogenation was observed to corrode the crystallites without changing in crystalline structure. Controllable room-temperature ferromagnetic (RT-FM) properties were obviously observed with hydrogenated WO₃ doped with Mn. In addition, there existed an optimum doping concentration of Mn in WO₃ to obtain superior FM properties. Therefore, Mn-doped WO₃ nanopowders, owning to these amazingly tunable magnetic properties, could be considered a potential candidate for many applications partially required FM properties such as optical phosphors and catalysts.     

Effects of sintering aid CuTa2O6 on piezoelectric and dielectric properties of sodium potassium niobate ceramics

In this study, the effects of a sintering aid CuTa₂O₆ (CT) on (Na_0.5K_0.5)NbO₃ (NKN) ceramics were investigated. The diffracted angles in XRD profiles decreased because the Nb-sites were replaced by Cu and Ta ions, causing the expansion of lattice volume. SEM images showed smaller grain sizes at a low concentration of CuTa₂O₆, and grain sizes increased as the concentration of CuTa₂O₆ doping increased because of a liquid phase formed. When CuTa₂O₆ dopants were doped into NKN ceramics, the T_O–T and T_c phase transitions decreased because the replacement of Ta⁵⁺ ions in the B-site. A high bulk density (4.595 g/cm³) and electromechanical coupling factor (k_p, k_t) were enhanced when CT dopants were doped into NKN ceramics. Moreover, the mechanical quality factor (Q_m) also increased from 67 to 1550. NKN ceramics with sintering aid CuTa₂O₆ doping showed excellent piezoelectric properties: k_p: 42.5%; k_t: 49.1%; Q_m: 1550; and d₃₃: 96 pC/N.     

Highly enhanced mechanical quality factor in lead-free (K0.5Na0.5)NbO3 piezoelectric ceramics by co-doping with K5.4Cu1.3Ta10O29 and CuO

Effects of Cu doping on the ferroelectric and piezoelectric properties of 0.0038 mol K_5.4Cu_1.3Ta₁₀O₂₉ modified (K_0.5Na_0.5)NbO₃ ceramics have been investigated. On the basis of analyses on crystal structure and polarization hysteresis, it is suggested that Cu ions reveal amphoteric doping behavior in KNN ceramics. At doping levels up to 1 mol%, the Cu ions substitute pentavalent B-site cations, acting as acceptors that generate O-vacancies to resultantly harden the ceramics. At doping levels above 1.5 mol%, however, Cu ions play a role as donors by replacing monovalent A-site cations. A specimen doped with 0.5 mol% CuO shows an extremely high mechanical quality factor of 3053, which is higher than those of any other reports on KNN-based ceramics.     

Low-thermal expansion polycrystalline tantalum tungstate ceramics

The synthesis of thermal-shock-resistant materials from the system Ta₂O₅WO₃ was investigated. Ta₂WO₈ had a very low unit-cell thermal expansion coefficient (+0.5 X 10^–6° C^–1). Ta₃₀W₂O₈₁ also had a relatively low coefficient (+4.0 X 10^–6 ° C^–1) and a thermal durability over 1600° C. The thermal expansion curves of these polycrystalline ceramics were lowered because of microcracks caused by the large thermal expansion anisotropy of the crystal axes and were accompanied by hysteresis loops. The densification of Ta₂WO₈ ceramic was promoted by the addition of some metal oxides, and the strong ceramic of Ta₃₀W₂O₈₁ was obtained by controlling grain growth.     

Electrical properties of Li2O-La2O3-SiO2 electrode glasses after Ta2O5 doping and Ta implantation

Electrical conductivities, , of the Li₂O-La₂O₃-SiO₂ glasses were investigated as functions of Ta₂O₅ doping and Ta ion-implantation. A linear relationship between logarithm and the inverse of the sample temperature, T, was found in 2 to 4 mol% Ta₂O5 doped Li₂O-La₂O₃-SiO₂ glasses. The conductivity increases as Ta₂O₅ content increases at sample temperatures above 100°C. Fluences of 50 keV Ta ions per cm² from 5 × 10¹⁶ to 2 × 10¹⁷ were implanted into 0% and 2% Ta₂O₅ containing Li₂O-La₂O₃-SiO₂ glass samples. The activation energy of the conductivity was deduced from the relation between log and 1/T. It was found in implanted samples that the conductivity increased, but the activation energy and T _k–100 decreased, where T _k–100 is the sample temperature when the conductivity reaches 100 × 10^–1 S/cm. However, the Ta₂O₅ containing implanted samples show higher conductivities, lower activation energies and lower T _k–100. X-ray photoelectron spectroscopy (XPS) was used to study the structural modification introduced by implantation. Bridging oxygen (BO) and non-bridging oxygen (NBO), were observed in all samples. The changes in relative concentrations of BO and NBO before and after implantation clearly indicate the structure modification which results in the increase of the conductivity. It was clearly demonstrated in this study that both doping Ta₂O₅ and implanting Ta ions enhance the conductivity of Li₂O-La₂O₃-SiO₂ electrode glasses.     

Structures and electrochromic properties of Ta0.3W0.7Ox thin films deposited by pulsed laser ablation

Electrochromic materials based on mixed metal oxides are of growing importance since improved durability, coloration efficiency and chemical stability, as well as a desirable neutral color could be accomplished in those multicomponent films. In this work, we have used the pulsed laser deposition technique to deposit thin films of Ta_0.3W_0.7O_x on ITO-coated glass substrates in reactive O₂ gas environment at a substrate temperature range of 200 to 700 °C. X-ray diffraction results showed that Ta_0.3W_0.7O_x films begin to crystallize to a cubic phase at substrate temperatures near 700 °C, while films with amorphous structure were obtained at lower substrate temperatures. The lattice constants of the polycrystalline films are similar to those of stoichiometric Ta_0.3W_0.7O_2.85 bulk materials. Optical transmittance of Ta_0.3W_0.7O_x films decreases as the O₂ pressures during deposition decreasing from 5.32 Pa to 0.13 Pa. Electrochromic properties of the Ta_0.3W_0.7O_x films were evaluated in 0.1 M H₃PO₄ electrolyte and the results were compared to those of WO₃ and Ta_0.1W_0.9O_x films deposited also by pulsed laser ablation. The results have demonstrated that the addition of one metal oxide (e.g., Ta₂O₅) into another (e.g., WO₃) is an effective way to alter the electrochromic properties of the individual constituents.     

Ultrathin TaOx film based photovoltaic device

Application of the economical metal oxide thin-film photovoltaic devices is hindered by the poor energy efficiency. This paper investigates the photovoltaic effect with an ultrathin tantalum oxide (TaOx) tunnel barrier, formed by the plasma oxidation of a pre-deposited tantalum (Ta) film. These ~ 3 nm TaOx tunnel barriers showed approximately 160 mV open circuit voltage and 3-5% energy efficiency, for varying light intensity. The ultrathin TaOx (~ 3 nm) could absorb approximately 12% of the incident light radiation in 400-1000 nm wavelength range; this strong light absorbing capability was found to be associated with the dramatically large extinction coefficient. Spectroscopic ellipsometry revealed that the extinction coefficient of 3 nm TaOx was ~ 0.2, two orders higher than that of tantalum penta oxide (Ta₂O₅). Interestingly, refractive index of this 3 nm thick TaOx was comparable with that of stochiometeric Ta₂O₅. However, heating and prolonged high-intensity light exposure deteriorated the photovoltaic effect in TaOx junctions. This study provides the basis to explore the photovoltaic effect in a highly economical and easily processable ultrathin metal oxide tunnel barrier or analogous systems.     

Influence of V2O5 additions to Ba(Mg1/3Ta2/3)O3 ceramics on sintering behavior and microwave dielectric properties

The microstructures and the microwave dielectric properties of barium magnesium tantalate ceramics prepared by conventional mixed oxide route have been investigated. The prepared Ba(Mg_1/3Ta_2/3)O₃ exhibited a mixture of cubic perovskite and a hexagonal superstructure with Mg and Ta showing 1:2 order in the B-site. It is found that low level doping of V₂O₅ (up to 0.5 wt.%) can significantly improve densification of the specimens and their microwave dielectric properties. The density of doped Ba(Mg_1/3Ta_2/3)O₃ ceramics can be increased beyond 95% of its theoretical value by 1500 °C-sintering, which is caused by the liquid-phase effect of V₂O₅ addition. The detected second phase Ta₂O₅ was mainly the result of V⁵⁺ substitution in the ceramics. Dielectric constant (ε_r) and temperature coefficient of resonant frequency (τ_f) were not significantly affected, while the unloaded quality factors Q were effectively promoted by V₂O₅ addition due to the increase in B-site ordering. The ε_r value of 24.1, Q×f value of 149,000 (at 10 GHz) and τ_f value of 7.2 ppm/°C were obtained for Ba(Mg_1/3Ta_2/3)O₃ ceramics with 0.25 wt.% V₂O₅ addition sintered at 1500 °C for 3 h.     

Preparation and characterization of Mn-doped BaTiO<Subscript>3</Subscript> thin films by magnetron sputtering

Barium titanate (BaTiO₃) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O₂/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural and electrical properties of BaTiO₃ thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure. Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped BaTiO₃ films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10⁻¹¹ A/cm⁻² at 6 kV/cm for 1% Mn-doped thin films.     

Conducting and topographic AFM analysis of Hf-doped and Al-doped Ta2O5 films

A conductive atomic force microscopy (C-AFM) has been used to study conductivity and electrical degradation of ultrathin (4 nm) Hf- and Al-doped Ta₂O₅ at the nanometer scale. The hardness testing has been also performed using the force measuring ability of the AFM. Since the size of the analyzed area is very small, features which are not visible by macroscopic tests are observed: extremely low leakage current (~ pA) up to significantly higher than the fields during standard current-voltage measurements; charge trapping/detrapping processes manifesting as current peaks at pre-breakdown voltages. Hf and Al addition improves the local conductivity of Ta₂O₅, provokes modification of the leakage current mechanism, and is effective in extending the potential of pure Ta₂O₅ as a high-k material at the nanoscale. The results point to a decisive role of the type of the dopant on the electrical and mechanical properties of the films and their local response to short term microwave irradiation. Hf-doped Ta₂O₅ exhibits excellent electrical stability and high hardness. Al doping provides more plastic films with large electrical inhomogeneities; the microwave treatment at room temperature is a way to improve these parameters to a level comparable to those of Hf-doped films.