The formation process of titania based nanorods during hydrothermal synthesis starting from an amorphous TiO2.nH2O gel has been investigated. Sodium tri-titanate (Na2Ti3O7) particles with a rodlike morphology were prepared by a simple hydrothermal process in the presence of a concentrated NaOH aqueous solution. The ion exchange reaction of the synthesized Na2Ti3O7 nanorods with HCl under ultrasonic treatment promotes a complete sodium substitution and the formation of H2Ti3O7 nanorods. Low-temperature annealing of the as-produced nanorods of Na2Ti3O7 and H2Ti3O7 leads to a loss of the layered crystal structure and the formation of nanorods of condensed framework phases-sodium hexa-titanate (Na2Ti6O13) and metastable TiO2-B phases, respectively. These transformations proceed without a significant change in particle morphology. The nanostructures were investigated by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET) method, thermogravimetric analysis (TGA), and Raman spectroscopy. The structural defects of the synthesized nanorods were investigated by high-resolution electron microscopy. The presence of planar defects can be attributed to the exfoliation of the zigzag ribbon layers into two-dimensional titanates as well as to the condensation of the layers of TiO6 octahedra into three-dimensional frameworks.

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Our first-principles computations show that the ground state of PbTiO3 under hydrostatic pressure transforms discontinuously from P4mm to R3c at 9 GPa. Spontaneous polarization decreases with increasing pressure so that the R3c phase transforms to the centrosymmetric Rc phase at around 27 GPa. The first-order phase transition between the tetragonal and rhombohedral phases is exceptional since there is no evidence for a bridging phase. The essential feature of the R3c and Rc phases is that they allow the oxygen octahedron to increase its volume VB at the expense of the cuboctahedral volume VA around a Pb ion. This is further supported by the fact that neither the R3m nor Cm phase, which keep the VA/VB ratio constant, is a ground state within the pressure range between 0 and 40 GPa. Thus, tetragonal strain is dominant up to 9 GPa, whereas at higher pressures, efficient compression through oxygen octahedra tilting plays the central role for PbTiO3. Previously predicted pressure induced colossal enhancement of piezoelectricity in PbTiO3 corresponds to unstable Cm and R3m phases. This suggests that the phase instability, in contrast to the polarization rotation, is responsible for the large piezoelectric properties observed in systems like Pb(Zr,Ti)O3 in the vicinity of the morphotropic phase boundary.

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Raman scattering studies of lead zirconate titanate Pb(Zr x Ti1-x )O3 (PZT), 0.10≤x≤0.80, and Nd-modified lead titanate Pb1-3y/2Nd y TiO3 (PNT), y=0.02, 0.10, bulk ceramics were carried out at ambient temperatures between 4.2 and 297 K. Our measurements reveal splitting of the E⊕B 1 symmetry peak at low temperatures in both PZT and PNT samples. Splitting or a very asymmetrical line shape of the three other E(TO) peaks in the PZT and PNT samples was also found. These findings are related to the precursor effects. We also discuss the phase stability of lead titanate based perovskites from the point of view of our experimental results and recent theoretical calculations. A simple model explaining the differences between the low-frequency Raman spectra of tetragonal and trigonal PZTs is outlined.

A water-soluble peroxititanic complex [Ti(OH) 3 O 2 ] 2 was prepared through the reaction between titanium metal and hydrogen peroxide at pH~11. A solution of lead nitrate and zirconyl nitrate was added to the peroxititanic acid solution, and a stoichiometric and amorphous precipitate of a mixed oxide of lead, zirconium and titanium was formed, which was filtered off and washed to eliminate nitrate ions. The precipitate was calcined between 600 and 1000 uC using a closed alumina boat. The precipitate was characterized by TG-DTA, ICP (Pb, Zr and Ti), elemental analysis (C, H, N and O), Raman spectroscopy and X-ray diffraction (XRD), and the calcined PZT powders were characterized by Raman spectroscopy and XRD. The amorphous precipitate showed a weight loss of 26% in the range from 30 to 500 uC, revealing that the crystallization process starts at low temperature. Rhombohedral Pb(Zr 0.60 Ti 0.40 )O 3 was obtained at temperatures above 900 uC. It is of particular importance that the use of the peroxititanic complex provided a method to synthesize PZT powders without the use of any organics (including alkoxides) or reagents containing undesirable halides.