Search results for "Titanate"

Céramiques diélectriques commandables pour applications micro-ondes : composites à base de titanate de baryum-strontium et d'un oxyde non ferroélectr…

2001

Since the last decades, dielectric ceramics have been considered as attractive for microwave applications as tunable dielectric resonators or phase shifters. For that, ceramic devices should be tunable – change in dielectric constant with applied voltage- with moderate to low dielectric constant (30 to 1000) and loss tangent as low as possible. To reconcile these properties, composite ceramics based on Ba0.6Sr0.4TiO3 (BSTO) and a non-ferroelectric oxide with a low dielectric constant (MgTiO3 or MgO) were synthesised. The aim of this study was to correlate the microstructure with the dielectric properties, especially the Curie temperature and the dielectric relaxation phenomena.Ceramics with…

On the harvest of rainfall energy by means of piezoelectric transducer

2013

In this paper a detailed study on the harvest of the energy contained in rainfall by means of piezoelectric transducers is presented. Diverse studies agree on the level of suitable generated voltage on the electrodes of a piezoelectric transducer subjected to rainfall, but a complete characterization on the supplied power is still missing. This work, in order to limit optimistic forecasts, takes into account the behavior of the transducers subjected to real and also artificial rainfall, condition that has shown promising behavior in laboratory. In order to increase the energy harvesting and also define its limits different loads have been taken into account. Only commercial transducers have…

Polar relaxation mode in pure and iron-doped barium titanate

1989

A dielectric relaxation peak is reported in ${\mathrm{BaTiO}}_{3}$ and in ${\mathrm{BaTi}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{O}}_{3}$. It is nearly monodispersive, centered in the ${10}^{8}$-Hz range, and slowest at the transition temperature ${T}_{c}$\ensuremath{\simeq}413 K from the cubic to the tetragonal phase. Iron doping lowers ${T}_{c}$ and slows down this relaxation mode.

Some Aspects of the Influence of Particle Size on Properties and Behaviour of a Dielectric Material : Example of Barium Titanate

1989

Anybody agrees with the idea that particle size plays an important role in the behaviour of a polycrystalline material but very few studies are giving precise information about this role. In this paper some experimental results are presented succintly to illustrate the importance of this physico-chemical factor. They are related to barium titanate, the main component of the dielectric material in the type II ceramic capacitors.

Electronics and Electromagnetism

2007

Synthesis of Lead Zirconate Antiferroelectric Thin Films by Sol-Gel Processing

2000

A modified methoxyethanol sol-gel process was used for the production of PbZrO3 thin films. The new route uses lead oxide [PbO] instead of lead acetate [Pb(OAc)2]. Through the use of this method it is possible to prepare single-phase perovskite materials with improved properties. Examples are given for PbZrO3 thin layers deposited by the spin coating process on TiO2/Pt/TiO2/SiO2/Si substrates from various sols where lead acetate or lead oxide are used as the starting lead compound. The preferred orientation and the perovskite phase content of the films were studied using X-ray diffraction analysis (XRD). Scanning electron microscopy (SEM) was used for microstructural characterization of the…

Influence de l'atmosphère gazeuse sur la cinétique de formation du titanate de baryum par réaction solide-solide

1986

International audience; Les études consacrées à la synthèse, par réaction solide-solide, du titanate de baryum (BaTiO3) ont montré l'importance des propriétés physicochimiques des solides initiaux (BaCO3 et TiO2) sur les propriétés du titanate obtenu. Lors de l'élaboration de céramiques diélectriques, il est en effet nécessaire d'éviter la formation de phases intermédiaires (Ba2TiO4, BaTi4O9, ...) qui nuisent à leurs propriétés diélectriques. La présence de ces phases peut être liée à une maîtrise imparfaite des nombreux paramètres influant sur la cinétique de la réaction. Le rôle de deux de ces paramètres : les traitements mécaniques et la nature de l'atmosphère gazeuse, fait l'objet de ce…

A new phase in ferroelectric oxides: The phase of charge transfer vibronic excitons

2001

It is shown, by means of Hartree-Fock-type calculations using the intermediate neglect of the differential overlap (INDO) method, that polaronic-type charge transfer vibronic excitons (CTVE) in ferroelectric oxides could lead to the formation of a new phase. The ground-state energy of this phase of strongly correlated CTVE lies within an optical gap of pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as ferroelectric and antiferromagnetic ordering. It is shown also that clusters of the CTVE phase being stabilized by oxygen vacancies could be responsible for the unusually strong optical Second Harmonic Generation (SHG) in nominally pure incipient ferroele…

Theoretical study of Fe doping and oxidation–reduction influence on the photorefractive effect in BaTiO_3

1993

We numerically solve charge-transport and Poisson equations for photorefractive BaTiO3 single crystals with a band model, using four impurity levels, Fe2+–Fe3+, Fe3+–Fe4+, VO••–VO•, and VO•-VOx. Densities and photoinduced spatial distributions of each population are computed as a function of annealing O partial pressure. Space-charge field and beam-coupling gain are also computed as a function of annealing O partial pressure, temperature, Fe concentration, grating wave vector, and light intensity. We discuss the intervening mechanism of impurity centers and the correlations between experimental conditions of crystal growth, oxidation–reduction treatments, and measurement parameters.

Local Structure Studies of Ti for SrTi16O3 and SrTi18O3 by Advanced X-ray Absorption Spectroscopy Data Analysis

2015

Strontium titanate is a model quantum paraelectric in which in the region of dominating quantum statistics the ferroelectric instability is inhibited due to nearly complete compensation of the harmonic contribution into ferroelectric soft mode frequency by the zero-point motion contribution. The enhancement of atomic masses by the substitution of 18O for 16O decreases the zero-point atomic motion and low-T ferroelectricity in SrTi18O3 is realized. In this study we report on the local structure of Ti in SrTi16O3 and SrTi18O3 by Ti K-edge extended x-ray absorption fine structure measurements in temperature range 6 – 300 K.