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Lead-free piezoelectric ceramics (1-x)K0.5Na0.5NbO3–xAgSbO3+0.75 mol % MnO2 were prepared by a conventional solid-state sintering technique, and the piezoelectric and dielectric properties of the ceramics were studied. The results of x-ray diffraction suggest that AgSbO3 diffuses into the K0.5Na0.5NbO3 lattices to form a new solid solution with a single-phase orthorhombic perovskite structure. After the addition of AgSbO3, the paraelectric cubic-ferroelectric tetragonal phase transition temperature (TC) and the ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperature (TO-T) decrease, and the ceramics become “softened,” resulting in significant improvements in the ferroelectric and piezoelectric properties. The ceramics with x=0.03–0.10 exhibit excellent piezoelectric properties: d33=130–216 pC/N, kp=0.44–0.51, and kt=0.40–0.52. The ceramics also exhibit a good thermal stability up to high TO-T, suggesting that the ceramics are promising candidates for lead-free piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics K0.5Na0.5NbO3+x mol % K5.4Cu1.3Ta10O29 have been prepared by a conventional ceramic fabrication technique. All the ceramics possess a perovskite structure with orthorhombic symmetry. Our results reveal that the addition of K5.4Cu1.3Ta10O29 is effective in improving the densification of the ceramics. Besides, after the addition of K5.4Cu1.3Ta10O29, the Curie temperature and the tetragonal-orthorhombic phase transition temperature decrease and the P-E loop becomes constricted, in particular, for the ceramic with x=0.75. Based on the symmetry-conforming principle of point defects, it is suggested that defect dipoles are formed by the acceptor dopant ions Cu2+ and O2- vacancies along the polarization direction. As a result of the low migration rate of defects, the defect dipoles remain in the original orientation during the P-E loop measurement and thus provide restoring forces to reverse the switched polarizations. Similarly, the defect dipoles do not response along with the polarization in the normal piezoelectric activities and thus provide “pinning” to the deformed polarization, making the ceramics become “hardened.” For the ceramic with x=0.75, the mechanical quality factor Qm becomes maximum at a value of 1530, while the other piezoelectric properties remain reasonably high: piezoelectric coefficient d33=90 pC/N, planar and thickness mode electromechanical coupling factors kP=41 and kt=46%. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics (1-x)K0.5Na0.5NbO3+xBaTiO3+y mol % CuO have been fabricated by an ordinary sintering technique. Our results show that the doping of CuO is effective in promoting the densification of the ceramics. With the doping of CuO, all the ceramics can be well sintered and exhibit a dense, pure perovskite structure. After the formation of a solid solution with BaTiO3, both the paraelectric cubic–ferroelectric tetragonal and ferroelectric tetragonal–ferroelectric orthorhombic phase transition temperatures decrease and a relax behavior is induced. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramics with 0.04≤x≤0.06 and y=1.00 at room temperature. Because of the more possible polarization states arising from the coexistence of the two phases and the improved densification, the piezoelectric and dielectric properties of the ceramics are enhanced significantly. The ceramic with x=0.06 and y=1.00 exhibits the optimum properties: d33=193 pC/N, kp=0.43, kt=0.40, and TC=314 °C. On the other hand, the ceramics with 0≤x≤0.01 and y=1.0 exhibit excellent “hard” piezoelectric characteristics: kp∼0.40, kt∼0.47, Qm∼1940, [variant_greek_epsilon]r∼230, and tan δ∼0.5%. [ABSTRACT FROM AUTHOR]

Lead-free ceramics (K0.5Na0.5)1-xLix(Nb1-yTay)O3 have been prepared by an ordinary sintering technique. Our results reveal that Li+ and Ta5+ diffuse into the K0.5Na0.5NbO3 lattices to form a solid solution with a perovskite structure. The substitution of Li+ induces an increase in the Curie temperature (TC) and a decrease in the ferroelectric tetragonal–ferroelectric orthorhombic phase transition temperature (TO-T). On the other hand, both TC and TO-T decrease after the substitution of Ta5+. A coexistence of the orthorhombic and tetragonal phases is formed at 0.0333=208 pC/N, electromechanical coupling factors kP=48% and kt=49%, remanent polarization Pr=14.2 μC/cm2, coercive field Ec=1.21 kV/mm, and Curie temperature TC=320 °C. [ABSTRACT FROM AUTHOR]

The effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6-xCaxTiO3 (0<=x<=0.3) has been studied. Powder x-ray diffraction revealed that the cubic lattice constant a decreases linearly with increasing x from 0 to 0.15, while showing an anomalous expansion between x=0.15 and x=0.18. This, together with the anomalies in the dielectric constants, Curie temperature TC, and elastic constants observed for 0.15C increases linearly with increasing x from 0 to 0.15; while deviating from linear behavior for x>0.15, TC increases persistently up to x=0.25 and thereafter shows a decrease. These variations of TC with x have been interpreted in terms of Ca-doping-induced A-site cation size variance, a substitution of a small amount of Ca ions for Ti ions, and structural phase separation. Upon cooling the longitudinal elastic constant CL shows drastic softening near TC, arising from the electrostrictive coupling between the polarization fluctuations and the elastic strains. Moreover, it was found that Ca doping induces the hardening of CL just below TC, and the magnitude of the relative hardening of CL (i.e., ΔCL/CL) increases with increasing x, implying that the tetragonal ferroelectric phase was increasingly stabilized by Ca doping. [ABSTRACT FROM AUTHOR]

(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-x PT) single crystals with x=0.24, 0.30, 0.31, and 0.33 have been investigated by spectroscopic ellipsometry. The refractive indices and extinction coefficients were obtained. The modified Sellmeier equations for the refractive indices were obtained by least-squares fit. The equations can be used to calculate the refractive index with high accuracy in the low absorption wavelength range, namely, from 400 to 5800 nm. The Sellmeier optical coefficients E0, λ0, S0, and Ed were calculated by fitting the single-term oscillator equation. They are related directly to the electronic energy band structure and have the physical significance. The optical band gap energies were also obtained from absorption coefficient spectra. Our results show that as the PT content increases, the refractive index of PMN-xPT single crystals increases, while the optical band gap energy decreases. Some discussions about the BO6 octahedron building block that determines the basic energy level of PMN-xPT single crystals are also presented in this article. [ABSTRACT FROM AUTHOR]

CuO-doped lead-free ceramics based on bismuth sodium titanate (Bi0.5Na0.5TiO3, BNT) and barium zirconate titanate (Ba(Zr0.07Ti0.93)O3, BZT) were prepared via a multi-step solid-state reaction process. The BNT–BZT with CuO dopant ceramics sintered at 1150–1180 °C for 2 h in air showed a pure perovskite structure. SEM images reveal that a small amount of CuO (<2 mol%) play a significant role on the microstructure to improve its sintering attributes, while it will degrade when the dopant is added beyond 2 mol%. The dielectric and piezoelectric properties of CuO-doped BNT–BZT ceramics were evaluated. At room temperature, the sample doped with 2 mol% CuO shows quite good properties such as a high piezoelectric constant ( d 33 ∼156.5 pC/N) and a high electromechanical coupling factor ( k t ∼52%). The depolarization temperature increased dramatically and the maximum permittivity temperature decreased slightly. [ABSTRACT FROM AUTHOR]

Heteroepitaxial barium strontium titanate (Ba0.7Sr0.3TiO3 or BST) thin films were successfully grown on (LaAlO3)0.3(Sr2AlTaO6)0.35 (LSAT) (001) using pulsed laser deposition. X-ray diffraction characterization revealed that the films have a good crystalline quality and a pure perovskite structure. The in-plane ferroelectric properties of the films were studied using interdigital electrodes (IDE). The film exhibited a ferroelectric state at room temperature with the remnant polarization Pr = 10.5 μC/cm2. A large linear electro-optic effect was observed in the Ba0.7Sr0.3TiO3 thin film in a transverse geometry at a wavelength of 632.8 nm using a modified Sénarmont method. The linear electro-optic coefficient rc of the Ba0.7Sr0.3TiO3 thin film was found to be 125.0 × 10-12 m/V, which is very promising for modulator applications. [ABSTRACT FROM AUTHOR]

Large plate-like Na0.5Bi0.5TiO3 (NBT) templates have been successfully synthesized from bismuth layer-structured ferroelectric Na0.5Bi4.5Ti4O15 (NBIT) particles by the topochemical method. Because of the highly anisotropic structure, plate-like NBIT particles were first synthesized by the molten-salt process. After the topochemical reaction with the complementary reactants (Na2CO3, and TiO2) in NaCl flux, the layer-structured NBIT particles were transformed to the perovskite NBT templates. The resulting NBT templates are large and of plate-like shape. Our results also reveal that they are more effective in inducing grain orientation in the BNKT-BT ceramics as compared with BIT templates. For a BNKT-BT ceramic textured with 20 wt% of NBT templates, it exhibits a very high degree of grain orientation and gives a large Lotgering factor of 0.89. [ABSTRACT FROM AUTHOR]

Epitaxial SrTiO3 thin films have been deposited on Si (100) substrates by laser molecular-beam epitaxy. The experiments have confirmed that the use of Sr buffer layer is essential for making high quality SrTiO3 film. Apart from this, processing parameters including the deposition temperature and time for each layer also have significant influence on the crystallinity and roughness of SrTiO3. The thin films prepared under optimized conditions were found to have a pure perovskite phase, well crystallized and epitaxially aligned. The electrical measurements indicate that the SrTiO3 film has a capacitance effective thickness of less than 16 Å. [ABSTRACT FROM AUTHOR]

Sol-gel-derived niobium (Nb)-doped lead zirconate titanate (PZT) films have been deposited on silicon substrates with a lead titanate seeding layer by the multiple-spin-coating technique. The doping level of Nb ranges from 0 to 2 mol%. With the seeding layer, the PZT films can crystallize well into the perovskite phase at a low temperature of 550°C for 2 h. The films are dense and have good dielectric and piezoelectric properties. Effective longitudinal and transverse piezoelectric coefficients (d 33,c and e 31,c ) of the films have been measured. Our results reveal that the Nb dopant effects on the PZT films are very similar to the experimentally-known effects on the corresponding bulk ceramics, i.e. enhancing both the longitudinal and transverse piezoelectric properties. For the PZT film doped with 1 mol% Nb, the observed values of d 33,c and e 31,c are 74 pm/V and 12.8 C/m 2 , respectively. [ABSTRACT FROM AUTHOR]

Lead lanthanum zirconate titanate (PLZT 9/65/35) thin films were deposited on MgO (00l) substrates using a sol–gel method. X-ray diffraction measurements reveal that the PLZT film has epitaxially grown on the substrate and has a pure perovskite structure. Using gold interdigital electrodes the in-plane dielectric properties of the films were measured as a function of frequency (1 kHz to 10 GHz), temperature (293–435 K) and dc electric field (0–20 MV/m). The PLZT (9/65/35) thin film exhibits a diffuse phase transition, which indicates a relaxor-like ferroelectric behavior. The temperature dependence of the characteristic relaxation time was analyzed in terms of the Vögel–Fulcher relation. The relative permittivity has a high tunability of 34–42% in the frequency range of 10 MHz to 1 GHz. [ABSTRACT FROM AUTHOR]

Ba0.5Sr0.5TiO3, Ba0.6Sr0.4TiO3, Ba0.7Sr0.3TiO3 and Ba0.8Sr0.2TiO3 thin films were fabricated by a modified sol-gel technique on Pt(111)/Ti/SiO2/Si(100) substrates. All BaxSr1-xTiO3 films crystallized in the perovskite structure with a crack free microstructure and clear grain boundaries. Highest relative permittivity and dielectric tunability was observed in the Ba0.7Sr0.3TiO3 thin film. Ba0.7Sr0.3TiO3 and Ba0.8Sr0.2TiO3 compositions demonstrated ferroelectric hysteresis loops indicating the presence of ferroelectricity at room temperature. The paraelectric compositions of Ba0.5Sr0.5TiO3 and Ba0.6Sr0.4TiO3 showed significant tunability with negligible loss tangent. The tunability of Ba0.5Sr0.5TiO3 thin film decreased with the increase of frequency from 100 kHz to 100 MHz. As the frequency increases, especially above 10 MHz, the relative permittivity decreases while the loss tangent increases. Since Ba0.5Sr0.5TiO3 thin film is paraelectric at room temperature, relaxation due to ferroelectric domains cannot occur. Therefore this behaviour has originated from the contact resistance and finite sheet resistance of both the bottom and top electrodes. To analyse the thin film capacitor, the parallel plate capacitor structure can be modeled based on an equivalent circuit, which contain electrode and contact resistance. [ABSTRACT FROM AUTHOR]

The temperature dependence of the dielectric permittivity of perovskite Ba(ZrxTi1-x)O3 solid solutions, PbMg1/3Nb2/3O3 relaxor, and BaTiO3 ferroelectric ceramics was measured. It is found that a Lorentz-type law can be used to describe the dielectric permittivity of either the normal ferroelectrics with or without diffuse phase transitions (DPT) or the typical ferroelectric relaxors. The ferroelectric DPT can be well described by just one fitting process using the Lorentz-type law, while the relaxor ferroelectric transition needs two independent fitting processes. The Lorentz-type law fails at the low temperature side of the dielectric maximum of a first-order ferroelectric phase transition. Above the transition temperature, the dielectric curves of all the studied materials can be well described by a Lorentz-type law. [ABSTRACT FROM AUTHOR]

Polycrystalline lead-free piezoelectric [Bi0.5(Na0.7K0.2Li0.1)0.5]TiO3 (BNKLT) thin films were grown on Pt/Ti/SiO2/Si substrates using pulsed laser deposition (PLD). In this letter, we report the ferroelectric properties and piezoresponse of the PLD-produced BNKLT thin films. X-ray diffraction characterization revealed a good crystallinity and a pure perovskite structure in the films. The films exhibited a well-defined polarization hysteresis loop with a remnant polarization Pr of 13.9 μC/cm2 and a coercive field Ec of 10.2 MV/m. The domain structure and its thermal-driven evolution from the ferroelectric to nonferroelectric phase were observed by piezoresponse force microscopy. The results were consistent with the phase transition profile of BNKLT bulk ceramics. Typical butterfly-shaped piezoresponse loop was obtained and the effective piezoelectric coefficient d33,f of the BNKLT thin films was about 64 pm/V. [ABSTRACT FROM AUTHOR]

Pb[sub 0.9]La[sub 0.1]Ti[sub 0.975]O[sub 3] (PLT10) thin films were deposited on SiO[sub 2]/Si(100) substrates coated with a ZrO[sub 2] buffer layer. Studies by x-ray diffraction and scanning electron microscopy reveal that the ZrO[sub 2] film consists of both tetragonal and monoclinic phases, with the tetragonal phase being the dominant one. The PLT10 film has a perovskite structure and the grains in the film have a rather uniform size of about 50 nm. By using interdigital transducer (IDT) electrodes the in-plane electrical properties, hysteresis loop, and pyroelectric coefficient of the PLT10 film were measured. The dielectric constant and loss factor vary only slightly with frequency in the range 10[sup 3]–10[sup 6] Hz, with the loss factor being less than 0.01 over the entire range. The leakage current density is lower than 2×10[sup -8] A/cm[sup 2] at a bias field of 5 kV/cm. The remnant polarization and coercive field are 12.6 μC/cm[sup 2] and 9.93 kV/cm, respectively. The film exhibits a reasonably high pyroelectric coefficient (95 μC/m[sup 2] K) after it has been poled by applying 120 V ac at 0.1 Hz across the IDT electrodes. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]