Preparation of Pb(Mg1/3Nb2/3)O3-PbTiO3 thin films by MOCVD using ultrasonic nebulization

Thin films of Pb(Mg_1/3,Nb_2/3)O₃ (PMN) and Pb(Mg_1/3,Nb_2/3)O₃-PbTiO₃ (PMN-PT) were fabricated on Si and Pt/Ti/SiO₂/Si substrates by MOCVD using ultrasonic nebulization and their characteristics were investigated. PMN-PT films deposited at 350^∘C were annealed in a RTA (Rapid Thermal Annealing) system at 650^∘C for 30 sec to improve the micostructural properties. The crystallographic properties of PMN-PT films strongly depend on the content ratio of PbTiO₃. The content of pyrochlore phase in PMN-PT films decreased with the increase of Ti content and nearly single phase perovskite films were obtained at the composition of 80PMN-20PT. The PMN-PT films with perovskite phase showed a typical butterfly type C-V curve which verifies the ferroelectricity and had the relative dielectric constant of about 60.     

Pb((Mg0.7Zn0.3)1/3Nb2/3)O3 Relaxor Ferroelectric Ceramics by a Reaction-Sintering Process

Pb((Mg_1/3Nb_2/3)_0.7(Zn_1/3Nb_2/3)_0.3)O₃ (PMZN) relaxor ferroelectric ceramics produced by a reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Mg(NO₃)₂, Zn(NO₃)₂ and Nb₂O₅ was pressed into pellets and sintered directly. PMZN ceramics of 100% perovskite phase were obtained. Density of 8.11 g/cm³ (> 98% of theoretical value) was obtained after sintered at 1200C for 2 h. 3–9 m grain size was obtained in PMZN ceramics sintered at 1180C–1250C for two hours by reaction-sintering process.Dielectric constant at room temperature under 1 kHz reaches 18200 after sintered at 1200C for 2 h.     

Epitaxial thin film heterostructures of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3

Abstract

We have grown stoichiometric pure perovskite phase Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) thin films and PMN-PT/SrRuO₃ heterostructures on miscut (100) SrTiO₃ substrates by pulsed laser deposition. X-ray diffraction θ–2θ scans show that the PMN-PT films are purely c-axis oriented. The off-axis Φ scans show that the heterostructures grow “cube-on-cube” with an in-plane epitaxial arrangement of PMN-PT[100], [010] // SrRuO₃[001] // SrTiO₃[100] and PMN-PT[010], [100] // SrRuO₃[110] // SrTiO₃[010]. The crystalline quality of the films found to be comparable to that of bulk single crystals. The AFM images show that the SrRuO₃ and PMN-PT layers have smooth surfaces with root mean square roughness of 9Å. These epitaxial heterostructures can be used for the fabrication of piezoelectric devices.     

Epitaxial ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 thin films on La0.7Sr0.3MnO3 bottom electrode

Epitaxial (001)-oriented 0.7Pb(Mg_0.33Nb_0.67)O₃-0.3PbTiO₃ (PMN-PT) thin films were deposited by pulsed laser deposition on vicinal SrTiO₃ (001) substrates using La_0.7Sr_0.3MnO₃ as bottom electrode. Detailed microstructural investigations of these films were carried out using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Polarization-field hysteresis curves were measured at room temperature. Spontaneous polarization P _s , remnant polarization P _r and coercive voltage V _c were found to be 25 μC/cm², 15 μC/cm² and 0.81 V, respectively. Field dependent dielectric constant measurements exhibited butterfly shaped curves, indicating the true ferroelectric nature of these films at room temperature. The dielectric constant and the dielectric loss at 100 kHz were found to be 238 and 0.14, respectively. The local piezoelectric properties of PMN-PT films were investigated by piezoelectric force microscopy and were found to exhibit a local piezoelectric coefficient of 7.8 pm/V.     

Ferroelectricity in Aurivillius-Type Structure Ceramics with n = 2 and (SrBi2Nb2O9)0.35(Bi3TiNbO9)0.65 Composition

Aurivillius-type structure compounds are good candidates for their use as high temperature piezoelectrics, due to their high ferro-paraelectric phase transition temperature. However, this characteristic correlates with a high coercive field that makes difficult the poling process, necessary to have piezoelectric activity. The electric properties, specially conductivity, limit the maximum poling field. On the other hand, piezoelectric properties are directly related to the ferroelectric remanent polarization. Thus, the study of both characteristics is towards improving the piezoelectric properties of these materials. In this work, ceramics with nominal composition (SrBi₂Nb₂O₉)_0.35(Bi₃TiNbO₉)_0.65 (T_C∼ 760^∘C), prepared by hot pressing of mechanically activated precursors, have been studied. The electrical properties (permittivity, dielectric loss factor and d.c. conductivity) as a function of frequency and temperature have been measured, up to temperatures higher than the ferro-paraelectric phase transition, and their anisotropy explained in terms of the ceramic texture. Well-saturated ferroelectric hysteresis loops at 250^∘C have been obtained, with values of P_r = 21.4 μ C/cm² and E_c = 70.4 kV/cm.     

Structure and Properties of Hot-Pressed Pb(Lu1/2Nb1/2)O3-PbTiO3 Binary System Ceramics*

Solid solution series of the (1 - x)Pb(Lu_1/2Nb_1/2)O₃ - x PbTiO₃ binary system ceramics (PLuNT) were synthesized and hot-pressed (temperature 950°C to 1130°C, pressure 25 MPa); its structure, dielectric and piezoelectric properties were studied. Pure lutecium niobate PLuN (x = 0) has a pronounced long-range order in the B-sublattice and an antiferroelectric to paraelectric phase transition at 258°C. The phase structure of the PLuNT system, at room temperature, changes from a pseudomonoclinic (psd-M, space group Bmm2) to tetragonal (T, space group P4mm). The pseudomonoclinic phase extends over the 0 x 0.38 interval within which the monoclinic angle proceeds a minimum near to 90° at x 0.2. The morphotropic region covers the interval x = 0.38 - 0.49, the concentration ratio psd-M:T 1 (the morphotropic phase boundary—MPB) corresponds to x = 0.41. Within the morphotropic region, a rather strong distortion of the unit cell—(c/a - 1) 0.02, 90.37º, characteristic of hard piezoelectrics is maintained. Dielectric dispersion and broadening of the phase transition, features typical to relaxors, are observed within the concentration interval of 0.1 x 0.3. The highest electromechanical coupling coefficients: k_p = 0.66, k_t = 0.48, k₃₁ = 0.34 of (1 - x) PLuN–xPT ceramics are attained in compositions near the MPB at x 0.41. Non-isovalent doping of PLuNT with La³⁺ in Pb sublattice shifts the MPB to lower values of x.     

Studies on Electrical Properties and Magnetoelectric Effect of (x)Ni0.8Cu0.2Fe2O4 + (1?x)Ba0.8Pb0.2Ti0.8Zr0.2O3 Composites

Materials consisting of piezomagnetic and piezoelectric phases viz. Ni_0.8Cu_0.2Fe₂O₄ and Ba_0.8Pb_0.2 Ti_0.8Zr_0.2O₃ have been prepared by standard ceramic method. The presence of two phases in the composites has been confirmed by XRD. Variation of the dielectric constant with frequency in the range 100–1 MHz has been studied at room temperature and the variation of dielectric constant with temperature at set frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) has been studied. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure. All the samples have shown linear magnetoelectric conversion in the presence of a static magnetic field. The dc resistivity (ρ_DC) was studied as a function of temperature in the range 300–773^∘K. The variation of resistivity with temperature shows metal/seconductor behaviour.