[en] PbZr_0.38Ti_0.62O_3 and PbZr_0.36Ti_0.64_O3 thick films deposited by screen printing on (0 0 0 1) single crystal sapphire substrates and prepared at two different sintering temperatures, were studied by Fourier-transform infrared reflectivity, time-domain TH_z transmission spectroscopy and micro-Raman spectroscopy. The dielectric response is discussed using the Lichtenecker model to account for the porosity of the films and to obtain the dense bulk dielectric functions. Results are compared with bulk tetragonal PZT 42/58 ceramics. The dynamic response in the films is dominated by an overdamped lead-based vibration in the TH_z range, as known in PZT, but its evaluated dielectric contribution is affected by the porosity and roughness of the surface. (Author)

[en] Phase transitions of sodium niobate, prepared by the solid state synthesis method, were examined using dielectric measurements, differential scanning calorimetry, and high temperature x-ray diffraction, in order to contribute to the clarification of its structural behavior below 400 deg. C. Four phase transitions were detected in the ceramic sample using dielectric measurements and differential scanning calorimetry and the obtained temperatures were in a good agreement with previous reports for the transitions of the P polymorph. The anomaly observed by dielectric measurements in the vicinity of 150 deg. C was frequency dependent and could be related to the dynamics of the ferroelectric nanoregions. The phase transitions of the as-synthesized NaNbO₃ powder were investigated using differential scanning calorimetry and high temperature x-ray diffraction. The results show the existence of the Q polymorph at room temperature, not previously reported for the powder, which undergoes a transition to the R polymorph upon heating through a temperature region between 265 and 326.5 deg. C. This transition is mainly related to the displacement of Na into a more symmetric position and a minor change in the tilting system. The structures at room temperature, 250, 300, and 420 deg. C were refined by the Rietveld method and the evolution of the tilting system of the octahedral network and cationic displacement are reported.

[en] Homogeneity of the amorphous sol-gel precursors of Pb(Zr,Ti)O₃ ferroelectric ceramics is studied at various Zr/Ti ratios. From Zr K-edge EXAFS spectra the immediate vicinity of Zr atoms is determined. A distorted octahedron of O atoms with all the bonds continued in Zr-O-Zr links is observed down to Zr/Ti ratio of 1:1, indicating the prevalent homocondensation of Zr. In the precursor with Zr/Ti ratio of 25/75 a smaller distortion of O octahedra is observed and heterometallic bonding Zr-O-Ti is found. Mixing of the two metals (Zr, Ti) at molecular level is thus established at low Zr/Ti ratios. (au)

No abstract available

[en] The analytical partial capacitance methods (PCM) widely accepted for calculation of properties of capacitors with planar electrodes, coplanar strip waveguides (CPS) and coplanar waveguides (CPW) are reviewed based on the challenges met during the development and tailoring of (Ba, Sr)TiO₃ thin films fabricated on different types of substrates. An alternative view on the conformal mapping method is given, a correction for electrodes of finite thickness is introduced and the applicability of easy-to-use simplified analytical equations is reviewed and extended. Calculation results obtained with different models are compared against the results of FEM numerical simulation in the parameter range relevant for development of tuneable ferroelectric films. The models were found to be less accurate than previously reported. Accordingly, guidelines for extending the applicability domain and for minimizing the inherent errors of the analytical models are presented. The discussion is focused on the possible improvements of the measurement techniques

[en] Single crystals of KNbO₃ and NaNbO₃ were selected from the limited number of suitable alkali compounds that are available and evaluated as possible reference materials for the electron-probe microanalysis (EPMA) of alkaline niobates with a composition described by the general formula K_1-xNa_xNbO₃. The EPMA study verified that KNbO₃ and NaNbO₃ single crystals are stable under the electron beam and compositionally homogeneous. A quantitative microanalysis confirmed the composition of pure KNbO₃, while the NaNbO₃ crystal contained 0.3 mass fraction % of Ca. A significant improvement in the accuracy of the quantitative EPMA of polycrystalline potassium-sodium niobates was achieved using these single crystals as standards. The crystals can also be useful as reference materials for the analysis of sodium and potassium in other materials. (author)

[en] A Pb(Mg_0.33Nb_0.67)_0.65Ti_0.35O₃ material system was synthesized by the sol-gel method; thin films were deposited via the spin-coating technique, and processed using the rapid thermal annealing. Effects of preparation parameters, such as annealing temperature and atmosphere, on the phase composition, microstructure and electrical properties were identified. Morphologically uniform and crack-free films were obtained. Among the obtained films, the highest k value was found to be 1425 for the 380 nm thick film that was annealed at 750 deg. C in O₂ indicating the suitability of this material system for ultrahigh-value capacitor applications.

[en] We have studied the low-temperature processing of ZnO by chemical solution deposition. A transparent, stable precursor solution prepared from zinc acetate dihydrate dissolved in 2-methoxyethanol was spin-coated on SiO_x/Si, soda-lime glass and polymer substrates and heated at 150 ^oC. Selected thin films deposited on SiO_x/Si were additionally heated at 450 ^oC. Microstructural and chemical analyses showed that the thin films heated at 150 ^oC in air were amorphous, contained no organic residues and had a root mean square roughness of 0.7 nm. The films deposited on SiO_x/Si and heated at 450 ^oC were crystallised and consisted of randomly oriented grains with a diameter of about 20 nm. All thin films were transparent, exhibiting a transmission of over 80% in the visible range. The resistivity of the 120-nm thick ZnO films processed at 150 ^oC was 57 MΩ cm and upon heating at 450 ^oC it decreased to 1.9 kΩ cm.

[en] Nanocrystalline powders and ceramics with controlled grain size from 15 to 3000 nm of PbMg_1/3Nb_2/3O₃(PMN) and (PMN)_0.65-(PbTiO₃)_0.35 (PMN-PT35) have been synthesized using the ball milling method. Dielectric experiments have revealed in PMN a disappearance of relaxation below ≅30 nm grain size and combined x-ray and Raman experiments the vanishing of correlations between polar nanoregions (PNRs). A similar study in morphotropic compound PMN-PT35 has shown the appearance of a relaxor state below ≅200 nm, associated to a destruction of the ferroelectric domains state towards PNRs in a paraelectric matrix. These phenomena are discussed in connection with pressure experiments from the literature and on the basis of polar states destabilization by both elastic and electric random fields changes associated with the size reduction

[en] The vast majority of studies on field-induced changes in (1–x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–xPT) materials at the morphotropic phase boundary (MPB) have been performed on single crystals, while the more complex responses in polycrystalline materials have not yet been resolved. By using combined microscopy and diffraction techniques, this study aims to determine the structural changes induced by application of an electric field to two representative MPB compositions of the PMN–xPT family, namely, PMN–30PT with the initial Cm and Pm coexisting phases, and PMN–35PT with the P4mm and Pm phases. Both ceramic compositions are characterized by a hierarchical domain structure with domains present at different length-scales. Based on the applied field measurements, major contributing effects in both compositions are outlined and discussed with respect to the processes related to the monoclinic phase and the adaptive phase theory. It is shown that the highly mobile domain walls are largely involved, along with the field-induced polarization rotation in the monoclinic PMN–30PT, and a phase transition to a mainly tetragonal structure in PMN–35PT. These multiscale results elucidate important aspects of field-induced changes in PMN–xPT materials, contributing to the understanding of the complex electrical and electromechanical response of relaxor ferroelectrics.