摘要:

Epitaxial barium strontium titanate and strontium titanate thin films were deposited on (100) MgO single-crystal substrates, utilizing Combustion Chemical Vapor Deposition. The as-deposited films were patterned with gold electrodes to form interdigitated structure to function as electrically tunable devices, namely, coupled microstripline phase shifters (CMPS). Microwave dielectric properties were characterized at 11–20 GHz with an applied electric field up to ±35 V/μm. A maximum figure of merit of 53°/dB at 20 GHz and 23°C was measured. The demonstrated high degree of tunability and relatively low loss showed great potential of these films for the targeted frequency agile device applications. Characterization, using SEM, EDS, and XRD, is presented in addition to microwave performance as a function of dc bias and frequency.

ISSN:1058-4587    

DOI:10.1080/10584580008216669

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The renewed interest in KTa1−xNbxO (KTN) mixed perovskite materials, especially in thin films of a high quality, is connected with their remarkable dielectric properties in the dilute compositions. Off-center Nb ions in the highly polarizable KTaO3lattice provide a drastic increase in the dielectric peak up to 20 times in comparison with pure KTaO3and KNbO3. This paper reports a continuation of KTN thin films studies with several Nb concentrations in the range of 0 ≤ x ≤ 1 prepared by pulsed laser deposition from segmented KTaO3, KNbO3and KNO3targets. The effect of the substrate and symmetry-breaking defects was studied by micro-Raman spectroscopy. An anomalous residual intensity of the forbidden first-order scattering modes in the cubic paraelectric phase of the KTN films was connected with the formation of polar microregions even far above the bulk Tcvalue. On the whole, the KTN film behavior shows the existence of specific defects enlarging the perovskite unit cell in the film so that the activity of off-center Nb ions increases in producing larger electric dipoles and extending the precursor phase above Tc.

ISSN:1058-4587    

DOI:10.1080/10584580008216670

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Spin coated Pb1−xLaxTi1−x/4Q3thin films (x' 0.00, 0.05.…0.30) on (0001) sapphire were studied using x-ray diffraction, atomic force microscopy, and Raman scattering in order to investigate the phase formation, surface morphology, and the phase transition behavior in them. The x-ray and Raman scattering reveal a decrease in tetragonality with La substitution in lead titanate. Microscopy estimated surface roughness was also found to be decreasing with the La doping. Raman scattering, in the temperature range 75–783K, shows the transition temperature about 730, 680, 614, and 563 K forx'0.05, 0.10, 0.15, and 0.20 compositions, respectively. The diffuse nature of the ferroelectric phase transition owing to a short-range structural disorder in the paraelectric cubic phase and an increase in the diffuseness with La doping indicates the relaxor behavior and its relationship with the local disorder in these materials.

ISSN:1058-4587    

DOI:10.1080/10584580008216671

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We have used Raman spectroscopy to investigate thin films of ferroelectric (SrBi2Ta2O9)x(Bi3TiNbO9)1−xlayered structures and to compare them with the corresponding bulk materials. Various compositions, with x ' 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, were prepared by metal organic solution deposition method on Pt/TiO2/SiO2/Si substrates. A topographic micro-Raman study revealed very homogeneous films at each composition. The Raman spectrum of x ' 0.0 film shows bands around 170, 232, 337, 522, 608, 677 and 832 cm−1, which indicates Bi3TiNbO9formation. The evolution of the Raman bands with the inclusion of SBT material shows frequency shifts and a broadening of the bands due to the differences in mass between Sr and Bi in the A-sites, and Ta, Ti, and Nb in the B-sites A lower degree of crystallization was found in the films compared to the bulk due to the presence of stress in the films. Strong contributions from defects were also observed in the temperature-dependent Raman spectra.

ISSN:1058-4587    

DOI:10.1080/10584580008216672

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Lanthanum doped lead titanate Pb1−xLaxTi1−x/4O3fibers (x '0, 5 and 15 at%) were grown by sol-gel technique and characterized for their phase formation behavior and crystal structure. The precursor sol was concentrated upon heating at 100°C to make it spinnable and used for fiber drawing. For heat treatment, a two-step heating schedule was designed on the basis of DSC analysis of the as drawn fibers. X-ray diffraction analysis showed that the tetragonality of the Lead Titanate (PT) fibers reduces with La doping and the structure is changed to pseudocubic from tetragonal. MicroRaman Spectroscopy confirms these observations of change in crystal structure and distortion in the material due to La doping. Dense and elongated grains of about 1 μm diameter were observed at the surface and at the cross section of PT fibers. La doped fibers show a porous fracture surface and also the grain size reduces dramatically with the addition of La. Strain energy is believed to play a major role in the observed changes in the microstructure.

ISSN:1058-4587    

DOI:10.1080/10584580008216673

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

SrTiO3films with thickness ranging from 25nn to 2.5μm were grown on LaAlO3substrates with SrRuO3electrode layers. Measurements of the dielectric properties were performed over a range of temperatures The dielectric loss depends strongly on the thickness, but differently above and below T ∼ 80 K. Our result suggests that, in the high temperature regime, the interfacial dead layer effect dommates while, in the low temperature regime, the losses related to the structural phase transition and quantum fluctuations are important. The contribution to the interfacial potential from Schottky barriers was investigated for different electrode materials. Preliminary results of this study suggest that the continued dielectric nonlinearity of the thin films at high temperatures (above T ∼ 80 K) complicates the analysis of the Schottky barrier height measurements.

ISSN:1058-4587    

DOI:10.1080/10584580008216674

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Ce doping improves the ferroelectric properties of sol-gel derived PZT thin films by facilitating easier domain wall movement. It also decreases the leakage current densities by reducing the concentration of free carriers through a decrease in concentration of Pb and O vacancies. Ce-PZT films retain good dielectric dispersion characteristics since the concentration of defects and defect dipoles are reduced. Ce doping dramatically improves the fatigue resistance of PZT thin films. We have studied the frequency dependence of fatigue behavior and shown that the loss of polarization due to fatigue follows a universal scaling behavior with N/f2, whereNis the number of the switching cycles andfis the frequency. The origin of the scaling is attributed to the drift of oxygen vacancies, which is the rate limiting process in the growth of the interface layer responsible for fatigue. Empirical fits for both undoped and cerium doped samples show that switchable polarization followsastretched exponential decay with time or N/f. Cerium doping is believed to improve fatigue resistance by impeding the motion of oxygen vacancies.

ISSN:1058-4587    

DOI:10.1080/10584580008216675

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Raman spectra have been measured in lead zinc niobate (PZN)- lead titanate (PT) solid solution single crystals (facets undefined) as functions of temperature (70K–580K) and composition (x ' 0.02, 0.085, and 0.11) into its parallel and perpendicular configurations. The presence of complex multiband Raman spectra is inconsistent withPm3mspace group symmetry and is an indication of short-range ordering on the B-site. Raman bandwidths are substantially large and nearly independent of temperature indicating a static structural disorder rather than a dynamic dipolar disorder. No soft mode like behavior is observed in the measured frequency range. Abrupt change in wavenumber (frequency) and width of certain bending mode (270 cm−1) at 410 K (140°C) is interpreted as an evidence for a reversible structural phase transition (C-R) at this temperature. The sequence of structural phase transition of C-T-R was also observed in one of the compositions (x ' 0.085), though diffuse and less obvious. In addition, the spectroscopic properties are found to be dependent on the substitution of titanium ion reflecting in the temperature of phase transition.

ISSN:1058-4587    

DOI:10.1080/10584580008216676

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Lead zirconate titanate (PZT) thin films with composition Zr/Ti ∼ 0.53/0.47 were deposited by the sol-gel technique. The films were characterized in terms of its polarization relaxation, fatigue and imprint characteristics. We have found that the polarization relaxation is due to the presence of a depolarization field which increases dramatically with the rise in temperature. Improved fatigue performance was observed when the film was fatigued with higher frequency. The direction of imprint depends on the state of polarization. With the increase in net polarization, the trapped charge density at the film-electrode interface increases which leads to imprint characteristics. Also the imprint increases considerably with the rise in temperature. Finally, we have made an attempt to correlate simultaneously fatigue, polarization relaxation, and imprint characteristics with the presence of mobile charge defects (viz. Vo) and defect dipoles (viz. VPb– Vo) in the film.

ISSN:1058-4587    

DOI:10.1080/10584580008216677

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The growth, microstructure and micro-Raman properties of SrBi2Tao0.8Nb1.2O9(SBTN) thin films deposited on Si(100) substrates using pulsed laser deposition (PLD) technique were studied at various substrate temperatures. Films were characterized using X-ray diffraction(XRD), atomic force microscopy(AFM), energy dispersive X-ray analysis (EDAX) and micro-Raman studies. AFM studies indicated that the average grain size of the films increased between 0.08 μm to 0.1 μm with the increasing growth temperatures. Micro-Raman studies of SBTN films revealed the fact that shifting of Raman modes corresponds to the BO6(where B' Ta/Nb) octahedral symmetry, to higher frequencies, is in accordance with the different masses of the B site atoms and the force constants involved due to Nb doping at Ta sites.

ISSN:1058-4587    

DOI:10.1080/10584580008216678

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor