Study of the tetragonal-to-cubic phase transition in PbTiO₃nanopowders

Abstract

The CPP (combined polymerization and pyrolysis) preparation route, in its enhanced liquid-precursor-based version, was combined with consecutive soft milling. For studies of temperature- and size-dependent structural changes occurring in ferroelectric lead titanate, this combined route yields a nanopowder series covering the relevant particle-size region at target quality. This material basis enables consistent SEM, TEM, XRD, Raman, EPR and dielectric measurements, which furnish a comprehensive picture of the cooperation between temperature rise and size reduction to eliminate tetragonality and concomitant ferroelectricity. Our previous original EPR studies on nanosized barium titanate are now extended to the lead titanate case. Furthermore, as compared to the pertinent literature standard, the materials basis is extended to powder samples of smaller mean particle sizes, comprising the critical size at which a PbTiO3 particle undergoes a transition into cubic paraelectric phase. Thus, the size-driven phase transition can be observed in a direct way (at 7 nm, which compares to 40 nm for BaTiO3), and the EPR data suggest a much less spacious gradient shell at the particle surfaces (thickness ≈ 2 nm) than in previous analogous investigations on BaTiO3 (15 nm).

Size effects in chromium-doped PbTiO3 nanopowders observed by multi-frequency EPR

“…16 Values of T C obtained by the temperature in which the permittivity ε' is maximal are in good agreement with T C derived from the EPR intensity measurements.…”

“…Alternatively, gradual reduction of mean particle size of the parent nanopowder up to 6 nm was done with the aid of a planetary ball mill under soft grinding conditions (low rotation frequency 360 min 1 , 6 ZrO 2 milling balls with diameter of 1 cm, milling times ranging from 5 min up to 2 days). 16 EPR spectra were taken at room temperature using the Bruker spectrometers ESP 380, EMX, and ELEXSYS E 600 in the X (9 GHz), Q (34 GHz), and W (94 GHz) band respectively. High-temperature experiments (X-band Varian E112 spectrometer) up to 830 K were carried out with a modified H 011 cavity, which is water-cooled and temperaturemonitored with a platinum wire resistance heating element.…”

General approach for the description of size effects in ferroelectric nanosystems

“…The substantial progress in synthesis of various ferroelectrics nanosystems, like epitaxial films [4], nanoparticles with controllable sizes [5], arrays of tubes and rods [6][7][8][9], the local characterization of their polar properties [10][11][12] and domain structure [13], triggered the renovation of interest to ferroic nanosystems theoretical description. It is worth to note the enormous achievements of both the phenomenological [14] and microscopic [15] theories, their recent advances in different fields like the description of nanorods [16,17], size effects in thin films [18,19], ferroelectric nanoparticles [20][21][22]; flexoelectric effect influence on the intrinsic properties [23,24] and response [25][26][27] of the nanosystems; the developed analytical model accounting for depolarization field as well as the formation of misfit dislocations [28][29][30].…”

Size effects of ferroelectric and magnetoelectric properties of semi-ellipsoidal bismuth ferrite nanoparticles

“…In particular Yadlovker and Berger [40,41,42] present the unexpected experimental results, which reveal the enhancement of polar properties of cylindrical nanoparticles of Rochelle salt. Frey and Payne [43], Zhao et al [44] and Erdem et al [45] demonstrate the possibility to control the temperature of the ferroelectric phase transition, the magnitude and position of the dielectric constant maximum for BaTiO 3 and PbTiO 3 nanopowders and nanoceramics. The studies of KTa 1-х Nb х O 3 nanopowders [46] and nanograin ceramics [47,48,49] discover the appearance of new polar phases, the shift of phase transition temperature in comparison with bulk crystals.…”