The nature of intrinsic and impurity point defects in lead zirconate titanate (PZT) ceramics has been explored. Using electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) methods, several impurity sites have been identified in the materials, including the Fe3+-oxygen vacancy (VO) complex and Pb ions. Both of these centers are incorporated into the PZT lattice. The Fe3+-V paramagnetic complex serves as a sensitive probe of the local crystal field in the ceramic; the symmetry of this defect roughly correlates with PZT phase diagram as the composition is varied from PbTiO3 to PbZrO3. NMR spectra 207Pb in PbTiO3, PbZrO3, and PZT with iron content from 0 to 0.4 wt% showed that increasing the iron concentration leads to a distortion of the crystal structure and to improvement of the electrophysical parameters of the piezoceramics. This is due to the formation of a phase which has a higher symmetry, but at high concentrations of iron (>0.4 wt%), it leads to sharp degradation of electrophysical parameters.

The nature of intrinsic and impurity point defects in lead zirconate titanate (PZT) ceramics has been explored. Using electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) methods several impurity sites have been identified in the materials, including Fe3+-oxygen vacancy (VO) complex and Pb ions. Both of these centers are incorporated into the PZT lattice. The Fe3+-VO paramagnetic complex serves as a sensitive probe of the local crystalline field in the ceramic; the symmetry of this defect is roughly correlated with PZT phase diagram as composition is varied from PbTiO3 to PbZrO3. NMR spectra 207Pb in PbTiO3, PbZrO3 and PZT with iron content from 0 to 0.4 mol % showed that increasing the iron concentration leads to a distortion of the crystal structure and improve the electrophysical parameters of the piezoceramics. This is due to the formation of the phase, which has a higher symmetry, but at high concentrations of iron (> 0.4 mol. %) leads to sharp degradation of electrophysical parameters.

Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR) spectra were studied in solvothermal- and citrate sol-gel-grown (CSGG) SrTiO3:Cr(0.1%) crystalline nanopowders. Various growth conditions and thermal treatments were used to determine defects and to tailor nanoparticles structure and crystallization processes. Solvothermal-grown nanopowders with 5 nm particle size revealed the dominant presence of the single perovskite-type phase. Annealing of the CSGG nanoparticles in air up to 800 degrees C leads to an increase of the particles size and the amount of the titaniumdioxide (rutile and/or anatase) phase, which is initially present in small amounts in CSGG powders. It was found that paramagnetic Cr3+, Cr5+, Cr3+ surf, O-, O2- ions are present in solvothermal- grown nanopowders and in all CSGG powders. In the annealed particles the majority of paramagnetic centers (PC) are located in the particle surface and in the TiO2 phase. The nature of the PC in nanopowders exhibiting different degrees of catalytic activity in nanopowders was studied too. A correlation between O- and O2- content, synthesis conditions and particle size was found. The NMR spectra of Ti-47 (I = 5/2) and Ti-49 (I = 7/2) reveal a pronounced dependence of the spectral line intensity on synthesis conditions, evidencing coexistence of Ti3+ and Ti4+ ions in SrTiO3:Cr nanoparticles. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Formation mechanisms of paramagnetic centers originating from Zr3+ and Cr3+ ions as well as the influence of composition of nanoparticles on thermogeneration processes of these paramagnetic centers in ZrO2 structure were studied. A set of nanosized powders of zirconium oxide was investigated by electron paramagnetic resonance method: nominally pure ZrO2; ZrO2 with Y2O3 and Sc2O3; ZrO2 with Cr2O3; ZrO2 with Y2O3 and Cr2O3. It is observed that the influence of annealing on EPR lines of Zr3+ and Cr3+ ions is different. Nuclear magnetic resonance data have shown that zirconium dioxide nanoparticles with Sc and Y impurities include two types of water molecules and two types of hydroxyl groups.

With the promise of electronics breakthrough, giant dielectric permittivity materials are under deep investigations. In most of the oxides where such behavior was observed, charged defects at interfaces are quoted for such giant behavior to occur but the underlying conduction and localization mechanisms are not well known. Comparing macroscopic dielectric relaxation to microscopic dynamics of charged defects resulting from electron paramagnetic resonance investigations we identify the actual charged defects in the case of BaTiO3 ceramics and composites. This link between the thermal activation at these two complementary scales may be extended to the numerous oxides were giant dielectric behavior was found.

In this work, we examine the size effect of dielectric susceptibility and pyrocoefficient in ferroelectric cone-shaped nanoparticles (nanocones). To solve the appropriate Euler-Lagrange equations, a direct variational method was used. In the limits of nanowires and thin films, our results coincide with previous results described in literature. We have shown that due to an enhancement of the ferroelectric-paraelectric transition temperature, pyroelectric response is expected far above the transition temperature bulk value.

We have studied the effect of the mechanical activation of the starting oxide mixture on the particle size of the resulting powders and the microstructure of electrostrictive lead magnesium niobate-lead titanate ceramics. The results demonstrate that reducing the grain size of the ceramics reduces their dielectric permittivity in both weak and strong electric fields, reduces their electrostrictive coefficient M 11, shifts the processes related to polarization saturation to higher electric fields, and increases the dielectric and electromechanical hystereses.

An ESR study is performed for four groups of zirconia nanopowder samples: nominally pure ZrO 2 powders (first group), zirconia samples with Y 2 O 3 and Sc 2 O 3 impurities (second group), samples with different amounts of Cr 2 O 3 (third group), and samples containing both Y 2 O 3 and Cr 2 O 3 (fourth group). The effect of annealing on ESR signals due to Zr 3+ ions (sample groups 1 and 2) and Cr 5+ ions (groups 3 and 4) is studied. It is established that, although the Zr 3+ and Cr 5+ ions have similar ESP characteristics, the annealing exerts different effects on ESR signals of these ions. Annealing in the temperature range 200–900°C leads to a monotonic increase in the amount of Zr 3+ ions. Interestingly, the annealing temperature at which Zr 3+ ions begin to generate ESR signals is different for samples with different impurity compositions. Unlike the Zr 3+ ions, the annealing curves of the ESR signals due to the Cr 5+ ions pass through an extremum at T = 500–600°C.

Ferroelectric size effects in cone-shaped nanoparticles (nanocones) are investigated for the first time. The Euler-Lagrange equations are solved using the direct variational technique. An approximate analytical expression is derived for the dependence of the ferroelectric phase transition temperature on the nanocone size. It is shown that the transition temperature for nanocones can be 2.5 times higher than the transition temperature for bulk materials.

Ferromagnetic spin-wave resonance has been observed in BiFeO3 nanoparticles with a size smaller than a critical size. The Heusler alloy Ni2MnGa has been studied too. The ferromagnetic resonance intensity of Ni2MnGa layers is much higher than that of BiFeO3. It is so high that even a single monolayer can be studied.

The effects of various external factors on the properties of nanosized zirconia particles are studied using electron paramagnetic resonance. It is shown that x-rays initiate radiation-stimulated oxidation of chromium impurity ions according to the scheme Cr3+ → Cr5+. Annealing of samples in hydrogen at temperatures in the range 250–650°C brings about a substantial decrease in the fraction of chromium ions in the Cr5+ charge state, but subsequent annealing of these samples in air leads to an increase in the Cr5+ fraction. Samples annealed in hydrogen generate a singlet EPR signal with the g factor of 2.0033 ± 0.0005 originating from electrically conducting regions which are formed on the surface of zirconia nanoparticles during their annealing in hydrogen.

ESR investigation of Sr1-xBaxTiO3 and Sr1-xCaxTiO3 at x = 0.01, 0.02, 0.04 and 0.06 was carried out in 3 cm frequency region at T = 300 K and T = 77 K. Die observed spectra were identified as originating from Mn4+, Cr3+, Fe3+ substituted for Ti4+. The investigation of the electronic structure was carried out by X-ray spectroscopy (XRS) and X-ray photoelectron spectroscopy (XPS). The valence band (VB) width was shown to be 22-24 eV It consists of two subbands. The Ti 3d-electrons and oxygen 2p-electrons contribute to the upper VB, while oxygen 2s-electrons contribute to lower VB.

ESR measurements revealed platinum impurity, which is incorporated in both pure and Ce-doped LPE films in the trivalent charge state (5d7) at the Al octahedral sites. There are 24 magnetically inequivalent positions of the platinum ion in the lattice, which most probably originate from three static Jahn–Teller distortions at each of the eight octahedral sites per unit cell. It was found that in LuAG LPE films the Ce3+ impurity substitutes only for Lu3+ sites. On the other hand, at least four different structural positions of the Ce3+ ions were clearly distinguished from measurements in the bulk LuAG crystals. Two of them correspond to the Ce3+ at Al octahedral sites.

We calculate the influence of surface tension on the barriers for oxygen ionic conductivity in nanograin ceramics. Namely, we evaluate the activation energy for diffusion of oxygen ions via its vacancies. In our model, latter vacancies have been considered as dilatational centers. We have shown, that the activation energy decreases with nanoparticle size decreasing. We derive the distribution function of activation energy on the base of distribution of nanoparticle sizes. We obtain analytical expressions for dependence of ionic conductivity on the temperature and nanograin sizes. The obtained expressions describe the observed behaviour of oxygen conductivity in nanograin ceramics of ZrO 2 :16% Y pretty good. Our theoretical studies show that the surface tension in nanoparticles is indeed a physical mechanism responsible for the essential enhancement of the oxygen ionic conductivity observed in nanograin samples, where the main contribution to the conductivity goes from the region near the particle surface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The EPR and proton magnetic resonance methods were applied to study zirconium hydroxide samples which transformed to nanoscale ZrO 2 powders upon annealing. The samples were obtained from solutions with mixture compositions (ZrO 2 + 0.5 mol % Cr 2 O 3 ) and (ZrO 2 + 3 mol % Y 2 O 3 + 0.5 mol % Cr 2 O 3 ). The influence of yttrium on the recharging of the chromium ion upon annealing of samples was studied in the temperature range 100–950°C. A significant influence of yttrium on internal stresses caused by heating and cooling in the lattice of nanoscale ZrO 2 particles was detected using the EPR method. It was shown that the typical features of the influence of yttrium on total (over the entire crystallite) and local (near chromium ions) lattice distortions depend on the sample heating temperature and are different for various annealing temperatures.

Using electron spin resonance (ESR), the lattice position and dynamic properties of Mn2+ ions were studied in 0.5 and 2 at. % manganese-doped SrTiO3 ceramics prepared by the conventional mixed oxide method. The measurements show that Mn2+ ions preferably (up to 97%) substitute for the Sr if the ceramics are prepared with a deficit of Sr ions. Motional narrowing of the Mn2+ ESR spectrum was observed when the temperature increased from 120 to 240-250 K, which was explained as a manifestation of the off-center position of this ion at the Sr site. From the analysis of the ESR spectra, the activation energy E-a=86 mV and frequency factor 1/tau(0)approximate to(1-5)10(13) s(-1) for the jumping of the impurity between symmetrical off-center positions were determined. Both are in agreement with those previously derived from the dielectric relaxation. This proves that the origin of the dielectric anomaly in SrTiO3:Mn is produced by the reorientation dynamics of Mn2+ dipoles.

The effect of surface tension on the activation energy for oxygen-ionic conduction in nanoceramics is considered. The activation energy is calculated for oxygen ion diffusion through oxygen vacancies, which are treated as dilatation centers. The activation energy is shown to decrease as the nanoparticle size decreases. Based on the size distribution function of nanoparticles, the activation energy distribution function is calculated. Analytical expressions are obtained for the dependences of the ionic conduction on temperature and nanoparticle size. The increase of two to three orders of magnitude in the oxygen-ionic conduction observed earlier in the ZrO2:16% Y nanoceramics is adequately described by these expressions. The surface tension of nanoparticles is shown to cause a substantial increase in the oxygen-ionic conduction observed in nanoceramics; the main contribution to the conductivity is related to a region near the particle surface.

Recently new incipient ferroelectrics with off-center ions SrTiO3 with Mn2+ substituted for Sr2+ was revealed (Tkach et. al PRB 73, 104113 (2006). Experimental investigation of Sr1-xMnxTiO3 properties, namely temperature, frequency and external electric field dependence of dielectric permittivity at different concentrations gave evidence about phase transitions induced by the impurities. However their nature was not found out up to now because of the absence of the theoretical analysis of the results. In this paper we performed such analysis by the theoretical description of the temperature of dielectric permittivity maxima dependence on Mn2+ concentration, the change of residual polarization with temperature, frequency and temperature dependence of the permittivity with Arrhenius and Vogel-Fulcher law at smaller and larger concentration respectively. The obtained results had shown that at x less than 0,03 and x between 0,15 and 0,03 the considered system Sr1-xMnxTiO3 is in dipole glass state and mixed ferroglass phase respectively.