Dielectric constant measurements have been performed in the ferroelectric lowtemperature phase of a KTa0.973Nb0.027O3 crystal. It is found that aging at a fixed temperature T pl induces a memory effect: the real part ε and the imaginary part ε of the complex dielectric constant ε around T pl remain weaker than they would be without aging, as long as the temperature stays below T pl ; on the contrary, a sojourn of the sample at temperatures higher than T pl rapidly erases the dips on ε and ε . Similarities with recent results obtained on two spin-glasses are emphasized and discussed.

Ancient ceramic wall tiles, called “azulejo”, firstly used on Portuguese churches, monasteries and palaces (15-18th century) have progressively been used in particular houses till the last century. These tiles and its use in huge decorative panels can be considered as a precious but fragile cultural heritage from Brazil to India, in several countries influenced by Portuguese culture. Morphologically, these tiles are composed by a porous clay-based ceramic body, the terracotta, covered by a protective glassy phase, the glaze. As artistic paintings, these murals incorporated various kinds of pigments in the glaze layer to create a pictorial impact on the walls of rich palaces or churches, real and durable monumental works-of-art. In the 21st century, degradation marks are visible on these ceramic tiles because of their use under corrosive conditions (moisture, atmospheric cycles…) along centuries. In order to promote their conservation and enhance their restoration, the physical-chemical characterization of the azulejos is performed in the present work, using mainly non-destructive processes like micro-Raman spectroscopy or X-Ray diffraction. In particular, Raman spectroscopy allows the detection of some nano/microcrystals present in the amorphous glaze due to pigments or opacifying agents or related to the elaboration process of the azulejo. Based on the observation of various selected fragments, one states that very few pigments have been used as colouring agents in this ceramic art during 17-18th centuries. Thus, the relationship between the different colours, the introduced pigments and the structural aspects of the glass will be focused. Some features related with the ancient ceramic technology will also be discussed.

We characterize in details the aging properties of the ferroelectric phase of K Ta1−x Nbx O3 (ktn), where both rejuvenation and (partial) memory are observed. In particular, we carefully examine the frequency dependence of several quantities that characterize aging, rejuvenation and memory. We find a marked subaging behaviour, with an a.c. dielectric susceptiblity scaling as ω √ tw, where tw is the waiting time. We suggest an interpretation in terms of pinned domain walls, much along the lines proposed for aging in a disordered ferromagnet, where both domain wall reconformations and overall (cumulative) domain growth are needed to rationalize the experimental findings. PACS. 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion -77-22-Gm Dielectric loss and relaxation -78-30-Ly Disordered solids

Raman spectroscopy results obtained for undoped and Aland/or Mn-doped ZnO thin films produced by RF-sputtering are reported. The effect of the doping method (either cosputtering or ion implantation), the dopant type, and its concentration on the Raman-active vibrational modes in these films were studied in detail. The results are discussed with focus on the peak shifts and broadening, and on the doping-induced relaxation of the symmetry selection rules. A particular attention is paid to the 520-530 cm À1 Raman band observed in all Mn containing samples and a simple theoretical model and arguments are presented in support of its relation to the local (gap) phonon mode produced by Mn atoms substituting Zn in the cationic sublattice of the ZnO crystal.

Transparent, conducting, Al-doped ZnO films have been deposited, by dc and pulsed dc magnetron sputtering, on glass and electroactive polymer (poly (vinylidene fluoride)-PVDF) substrates. Samples have been prepared at room temperature varying the argon sputtering pressure, after optimizing other processing conditions. All ZnO:Al films are polycrystalline and preferentially oriented along the [002] axis. Electrical resistivity around 3.3x10-3 Ω.cm and optical transmittance of ~85% at 550 nm have been obtained for AZOY films deposited on glass, while a resistivity of 1.7x10-2 Ω.cm and transmittance of ~70% at 550 nm have been attained in similar coatings on PVDF. One of the main parameters affecting film resistivity seems to be the roughness of the substrate.

PACS. 77.22.Gm Dielectric loss and relaxation – 78.30.Ly Disordered solids,

Return to disorder, and less frequently memory, have been demonstrated in various disordered materials. In order to find the conditions necessary for the observation of these effects, the evolution of the real part ´ of the dielectric constant of two disordered paraelectric crystals K1-x Lix TaO3 (KLT) has been extensively studied by the means of the capacitance C (T , t ) around the beginning and the end of a temperature plateau. The return to disorder and memory effects have not been seen in KTL, in contrast to what was recently observed in disordered ferroelectric crystals KTa1-y Nby O3 of a similar family. The variations dC = P (T 0 , t 0 ) dT + Q (T 0 , t 0 ) dt in the vicinity of the point (T 0 , t 0 ) are split into a contribution depending on temperature only and an isothermal contribution only depending on time. All the results of such an analysis of the features observed in KLT can be explained by the domain wall model in its original form.

A Raman spectroscopy study of doped versus undoped ZnO layers is presented. The layers were grown by RF magnetron sputtering and the doping with Al, Sb and Mn was achieved by ion implantation with subsequent annealing. First‐order Raman response measured under λ=488 nm excitation is discussed. It is shown that doping with any of the impurities used in this work produces a strong enhancement of the longitudinal optical (LO) phonon band, which is attributed to the intra‐band Fröhlich mechanism. In addition, doping with Mn results in an extra mode located at 530 cm‐1, tentatively attributed to a local vibrational mode of Mn substituting Zn in the lattice sites. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)