PbTiO

Simple ABO compounds in addition to BaTiO are cadmium titanate [12014-14-17, CdTiO lead titanate [12060-00-3] PbTiO potassium niobate [12030-85-2] KNbO sodium niobate [12034-09-2], NaNbO silver niobate [12309-96-5], AgNbO potassium iodate [7758-05-6], KIO bismuth ferrate [12010-42-3], BiFeO sodium tantalate, NaTaO and lead zirconate [12060-01 -4], PbZrO. The perovskite stmcture is also tolerant of a very wide range of multiple cation substitution on both A and B sites. Thus many more complex compounds have been found (16,17), eg, (K 2 i/2) 3 ... 

Certain perovskites with Pb on the A site are particularly important and show pronounced piezoelectric characteristics (PbTiO, PZT, PLZT). Different responses are found in BaTiO and PZT to the addition of donor dopants such as La ". In PZT, lead monoxide [1317-36-8] PbO, lost by volatilization during sintering, can be replaced in the crystal by La202, where the excess positive charge of the La " is balanced by lead vacancies, leading to... 

In lead zh conate, PbZrOs, the larger lead ions are displaced alternately from the cube corner sites to produce an antifeiToelectric. This can readily be converted to a feiToelectric by dre substitution of Ti" + ions for some of the Zr + ions, the maximum value of permittivity occumirg at about the 50 50 mixture of PbZrOs and PbTiOs. The resulting PZT ceramics are used in a number of capacitance and electro-optic applicahons. The major problem in dre preparation of these solid soluhons is the volatility of PbO. This is overcome by... 

Figure 14 shows the result of a Brillouin scattering experiment in the vicinity of Tc [11]. Closed circles and open circles below Tc indicate the modes split from the doubly degenerated ferroelectric soft mode. The closed circles above Tc denote the frequency of the doubly degenerated soft u mode in the paraelectric phase. The results clearly show a softening of the soft mode toward zero frequency at Tc following the Curie-Weiss law. The soft mode remains underdamped even at Tc. Generally, a soft mode is heavily damped in the vicinity of Tc, e.g., as for PbTiOs, which are typical displacive-type... 

Figure 8.1 Equilibrium phase diagram of the PbTiOs (001) surface as a function of temperature and PbO partial pressure. Solid lines separate observed phase fields corresponding to PbO condensation, c(2 x 2), and 1x6 reconstructions. Dotted lines are literature values [7] for the PbO condensation and PbTiOs decomposition boundaries.

Figure 8.2 Oscillations in the 20L ctr intensity at L = 0.5 from evolution of thickness fringes during addition of 9 unit cells to 1-unit-cell-thick PbTiOs film. Vertical dashed lines indicate beginning and end of growth.

A primary focus of our work has been to understand the ferroelectric phase transition in thin epitaxial films of PbTiOs. It is expected that epitaxial strain effects are important in such films because of the large, anisotropic strain associated with the phase transition. Figure 8.3 shows the phase diagram for PbTiOs as a function of epitaxial strain and temperature calculated using Landau-Ginzburg-Devonshire (lgd) theory [9], Here epitaxial strain is defined as the in-plane strain imposed by the substrate, experienced by the cubic (paraelectric) phase of PbTiOs. The dashed line shows that a coherent PbTiOs film on a SrTiOs substrate experiences somewhat more than 1 % compressive epitaxial strain. Such compressive strain favors the ferroelectric PbTiOs phase having the c domain orientation, i.e. with the c (polar) axis normal to the film. From Figure 8.3 one can see that the paraelectric-ferroelectric transition temperature Tc for coherently-strained PbTiOs films on SrTiOs is predicted to be elevated by 260°C above that of... 

Figure 8.3 Phase diagram for epitaxially-strained PbTiOs calculated using Landau-Ginzburg-Devonshire theory [9]. The dashed line shows the epitaxial strain corresponding to a SrTiC>3...

Figure 8.4 Sequence of in-plane scans through the PbTiOs 304 peak at various temperatures, showing the development and disappearance of satellites in the diffuse x-ray scattering as temperature is lowered (19.2 nm thick film).

Figure 8.5 Typical in-plane distributions of diffuse x-ray intensity around the PbTiOs 304 peak, for various film thicknesses and temperatures. Darker shade indicates higher intensity (log scale). Elongation of central Bragg peak is due to asymmetric resolution function.

Figure 8.6 Stripe period as a function of temperature for various thickness PbTiOs films, showing transition between Fa and h p stripe phases.

Figure 2. Gives 7], function of PbTiO, ultra fine particles in terms of equation (6) and experiment results of the specific heat measurements the symbol derived from Ref [10], a derived from ref [11]. The solid line is our model and the dash line is a mechanic and thermodynamic model in reference [1].

Materials of particular interest are the perovskite oxides BaTiOs-SrTiOs (BST) and PbZrOs-PbTiOs (PZT) solid solutions as well as the layered perovskites based upon SrBi2Ta209 (SBT). Since the ferroelectric effect requires... 

Another general class of solids that has been prepared as thin films using PLD is ferroelectric materials. A potentially useful characteristic of ferroelectric materials is that they can be polarized by an electric field and retain this polarization when the field is removed. In ferroelectric thin films it may be possible to exploit this polarization phenomenon to make sensors, displays, and memory devices. A number of techniques have been used to prepare ferroelectric thin films. However, it has been difficult to control the stoichiometry (and correspondingly the properties) of these materials using thermal and sputtering techniques. In part, the difficulty in maintaining correct stoichiometry is due to the volatility of a component in the material (e.g. Pb in PbTiOs). 

PLD of crystalline and stoichiometric ferroelectric materials has been successful for a number of materials. For example, crystaUine PbTiOs thin films have been deposited at only 350 °C using a KrF excimer laser (A. = 248 mn). The low deposition temperature makes this a potentially attractive method for directly fabricating ferroelectric/semiconductor hybrid devices. A related solid that is more difficult to prepare in thin film form is PbZri- ThOs. To maintain the Pb stoichiometry and ensure random mixing of Ti and Zr requires careful control of film synthesis conditions. ... 

The inverse-micelle approach may also offer a generalized scheme for the preparation of monodisperse metal-oxide nanoparticles. The reported materials are ferroelectric oxides and, thus, stray from our emphasis on optically active semiconductor NQDs. Nevertheless, the method demonstrates an intriguing and useful approach the combination of sol-gel techniques with inverse-micelle nanoparticle synthesis (with OTO erafe-temperature nucleation and growth). Monodisperse barium titanate, BaTiOs, nanocrystals, with diameters controlled in the range from 6-12nm, were prepared. In addition, proof-of-principle preparations were successfully conducted for Ti02 and PbTiOs. Single-source alkoxide precmsors are used to ensure proper stoichiometry in the preparation of complex oxides (e.g. bimetallic oxides) and are commercially available for a variety of systems. The... 

Lattice dynamics in bulk perovskite oxide ferroelectrics has been investigated for several decades using neutron scattering [71-77], far infrared spectroscopy [78-83], and Raman scattering. Raman spectroscopy is one of the most powerful analytical techniques for studying the lattice vibrations and other elementary excitations in solids providing important information about the stmcture, composition, strain, defects, and phase transitions. This technique was successfully applied to many ferroelectric materials, such as bulk perovskite oxides barium titanate (BaTiOs), strontium titanate (SrTiOs), lead titanate (PbTiOs) [84-88], and others. 

Synchrotron X-ray scattering results indicated the presence of 180° domains in the 2.4, 4.0, and 10-nm-thick BaTiOs films capped with 10-nm SrTiOs. Similar to the results obtained for PbTiOs films [38, 156], diffuse intensity induced by the periodic nature of the ferroelectric 180° domains appeared in the scattering around the BaTiOs Bragg peaks [48]. In particular, for the 10-nm-thick capped film the diffuse intensity was absent at 950 K, but it was present at 870 K and below, yielding a Tc value consistent with Raman results. Similar diffuse scattering was observed for the 4.0- and 2.4-nm-thick capped samples at room temperature, while... 

Rabe KM, Waghmare UV (1996) Strain coupling in the PbTiOs ferroelectric transition. Philos Trans R Soc Lond A354 2897... 

Le Marrec F, Farhi R, El Marssi M, Dellis JL, Karkut MG, Ariosa D (2000) Ferroelectric PbTiOs/BaTiOs superlattices growth anomalies and confined modes. Phys Rev B 61 R6447... 

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