BaTiO single crystal

In a recent letter the first NMR observation of quadrupole coupling induced Ti and Ti satellites in the cubic phase of an ultrapure BaTiOs single crystal above the ferroelectric transition was presented [8]. 

Figure 15.13 (a) Crystallographic changes in BaTi03 as a function of temperature. b) Temperature dependence of relative dielectric constant of BaTiO, single crystal, for the c and a axis, (c) Temperature dependence of the saturation polarization for polycrystalline BaTi03. Note similarity between this figure and Fig. 15.4/>. 

In Fig. 3.32, one can see the room temperature EPR spectra of Fe + paramagnetic centers substituted for Ti + ions in BaTiOs nanopowders. The mean size of the particles decreased from several hundreds nm to several tens nm at annealing temperature decrease from 1,350 to 900 °C [101]. It has been established, that in some samples the size distribution function has one peak while in the other ones it has two peaks In particular, fc the sample annealed at 900 °C, these two peaks positions were R 40 nm and R 140 nm. In Fig. 3.32, the calculated powder spectrum is reported. The spectrum has been calculated with the help of spin-hamiltonian parameters measured earlier for Fe + in BaTiOs single crystals [106]. It follows from Fig. 3.32, that the spectrum for the largest particles (about pm) contains all the transitions inherent in bulk samples so that the powders consisting of micron size particles can be considered as bulk ones. The cubic symmetry line... 

A. L. Gruverman, J. Hatano, and H. Tokumoto, Scanning Force Microscopy Studies of Domain Structure in BaTiOs Single Crystals, Jap. J. Appl. Phys. 36, 2207 2211 (1997). 

Figure 11.17. Hysteresis loop for a BaTiOs single crystal...

Single crystal and bulk BaTiOs exhibits a sharp paraelectric-to-ferroelectric transition at 393K. In the presence of submicron grains, the transition becomes diffuse and can be absent for polycrystalline BaTiOs. Twin boundaries along the four crystallographically equivalent 11 planes constitute the main lattice defects. Junctions between such twin boundaries can be frequently observed within a grain. The local atomic arrangement of the core of twin intersections was studied by focal-series reconstruction (Jia etal. 1999). 

Barium titanate crystals rank high among those solids on which electronic research has been focused during the last two decades, because this compound and its derivatives belong to a promising group of ferroelectrics. The properties of single crystals of BaTiOs reveal that the crystals are not uniform they respond to an electrical field as if they have a skin which covers the bulk of the crystal. 

The value of of the BaTiO, ceramics is lower than that reported for BaTiOj single crystal [9] (along [100] =4 000). This may be due to the structural and compositional variances. Meanwhile, the size of crystalline particle may affect the dielectric constant , that is, when the particle size is lower than certain value, the constant will decrease with the decrease of the size. In addition to those mentioned above, porosity and the existence of low dielectric constant affect the non-ferroelectric layers at the metal-ferroelectric interface and the grain boundaries. 

Describe the phases that you expect to form as a liquid of composition BaTiOs is cooled down to room temperature. Given the statement we make in Section 8.10 about the growth of single crystals of cubic BaTiOs, what factors besides thermodynamics determine our ability to grow single crystals ... 

Polycrystalline lanthanum-doped BaTiOs (BLT) is one example of a PTC material. The effect is associated with GBs and is not observed in single crystals. At the GB there is a potential barrier (( )) preventing electron movement from one grain to an adjacent one (very similar to that caused by the IGF in ZnO). The GB resistance, i gb is... 

Barium titanate is ferroelectric and, by implication, also pyroelectric and piezoelectric. The characteristic of a ferroelectric is that it is polarized in the absence of an applied electric field and the direction of polarization can be reversed. Figure 31.10 shows a rectangular hysteresis loop for a singledomain single crystal of BaTiOs. This loop was obtained at room temperature using a 50 Hz supply. 

Figure 31.14 shows the temperature dependence of the dielectric constant of single-crystal BaTi03. The high value of k appears over a very short temperature range, close to 0c and far from room temperature. For this reason pure BaTiOs is not particularly useful as a dielectric. Ideally k must be... 

FIGURE 31.10 Hysteresis loops for BaTiOs. (a) Single-domain single crystal, (b) Polycrystalline ceramic. 

FIGURE 31.14 (a) Dielectric constant and (b) spontaneous polarization of single-crystal BaTiOs as a function of T. (Compare to Figure 31.9.)... 

Explain why the hysteresis loops of single crystal and polycrystalline BaTiOs shown in Figure 31.10 have different and P. Would you expect this behavior ... 

Figure 15.12. Growth of a PblMgipNbj/jIOj-SSPbTlOj (mol%) (PMN-PT) single crystal into a fine (PMN-PT)-2Li20-6Pb0 (mol%) matrix from a BaTiOs seed crystal during annealing at I200°C for 50 h. Some abnormal grains are visible In the matrix.

H.S. (2005) Fatigue crack growth for BaTiO ferroelectric single crystals imder cyclic electric loading./. Am. Ceram. Soc.,... 

Single-crystal materials, however, are very expensive and in some cases impossible to fabricate. In response to this challenge, polycrystalline ferroelectrics with controlled crystallographic textures attempt to match, and in some cases overcome the limitations of their single-crystal counterparts. Figure 3 summarizes the results for two chemistries, BaTiOs and PZN-PT, as reported in [82]. Here,... 

Barium titanate has been studied extensively since the end of World War II when it was identified independently in Russia, Japan and USA as a promising material with high permittivity for ceramic capacitors. Its ferroelectric activity is known since 1946 when it was discovered on ceramic samples. Since 1950 s also the single-crystals of desired size and quality are available. BaTiOs undergoes several phase transitions... 

Remeika, J.P. (1954) A method for growing barium titanate single crystals, J. Am. Chem. Soc. 76, 940. Growth of BaTiOs by flux growth at Bell Labs. 

The hysteresis loop of a polycrystalline BaTiOs ceramic has a higher and lower Pr than the single crystal. 

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