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The ferroelectric solid solutions described by a general formula 0.98Pb(Zr1-xTix)O3 – 0.02La(Fe3+0.5, Nb5+0.5)O3 have been obtained by solid state reaction technique, where x assumes the following values: 0.42, 0.48 and 0.58. The structure of these ferroelectric compositions has been investigated in detail using X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM). The results obtained by XRD have evidenced that all obtained samples have a perovskite structure. The influence of the sintering temperature on the degree of incorporation of the elements in the solid solution have been studied too. The dielectric and piezoelectric constants have been determined and the influence of temperature on obtained values are presented and discussed. The performed experimental results have pointed out that the materials are characterized by a high anisotropy. Furthermore, the obtained values of the electromechanical coupling factor (kp) is situated between 0.40÷0.65 depending on the composition and the sintering temperature too.

The influence of the sintering temperature on the structure and on the hysteresis loops of Fe3+ doped Pb(ZrxTi1-x)O3 system has been investigated. Three compositions have been selected in the following mode: one in rhombohedral region, one in MPB region and one in tetragonal region have been obtained by solid state reaction technique. Sintering has been carried out at 12000C and 12500C respectively. The nature of the phases has been investigated in detail using X-ray diffraction analysis (XRD). All the sintered samples reveal a perovskite type structure. The surfaces have been lapped and metalized in order to obtaine the hysteresis loops at room temperature. The results showed a similar behaviour with “hard” PZT ceramics.

In the present paper (1-x)Pb (Zr1-yTiy)O3 – xPb (Mn1/3Sb2/3)O3 – z at%E system, with E = Pr3+, Nd5+ and Gd3+ where x = 0.12; y = 0.48; z = 0 and 0.02 ceramic synthesized by solid state reaction technique is analysed. The investigation aims studying of the effect of dopants on the dielectric and piezoelectric properties of such piezoelectric ceramic. The prepared powders have been uniaxially pressed into discs with diameter of 10 – 12 mm and thickness of 1.2 mm. Sintering has been carried out in air atmosphere at temperatures of 1150°C and 1200°C, respectively, for 2 hours each, followed by a controlled cooling at a rate of 200°C /h. The piezoelectric properties have been investigated after a suitable preparation, including polishing, metallization. The structure of the samples has been determined by X-ray diffractometry (XRD), while the morphology and grains size have been investigated by the scanning electron microscopy (SEM). The piezoelectric properties have been studied by the resonance - antiresonance method. XRD analysis reveals a perovskite tetragonal structure and, as expected for ceramic materials, SEM analysis indicates that the average grain size increases as sintering temperature increases. The dielectric and piezoelectric properties have been determined measuring the ceramic discs, and properties, as dielectric permittivity (εr), dielectric loss (tg δ), and the electromechanical coupling factor (kp) have been obtained. The acquired results indicate a significant effect of the dopants on the dielectric and piezoelectric properties of such materials.

In this paper, some compositions described by the general formula Pb(ZrxTi1-x)0.99Fe0.01O3 have been considered and investigated. The compositions considered have been obtained by solid state reaction technique, where x corresponds to 0.42, 0.52 and 0.58. Sintering has been performed for 2 hours at temperatures between 1100oC and 1250oC. The influence of the sintering temperature on the microstructure and on the hysteresis loops of Fe3+ doped Pb(ZrxTi1-x)O3 system has been investigated. The crystallographic phase and microstucture of the sintered compositions have been studied in detail using X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM). The experimental results obtained by XRD have revealed that all the sintered samples have a perovskite structure. In order to correlate the behavior of the sintered materials to their microscopic structure, the domain structures have been defined by SEM. The dielectric properties, as relative dielectric permittivity (εr) and dielectric loss (tan δ) have been measured. The hysteresis loops at room temperature of all un-poled sintered compositions reveal a similar behaviour with “hard” PZT ceramics. The piezoelectric properties like electromechanical coupling factor (kp) have been investigated after polarization.

This paper reports, the studies on chemical transformations at thermal treatment of a mixture of SrCO3 and Co3O4 corresponding to stoichiometric ratio of SrCoO3 compound. The mixture of raw materials was prepared by mechanical activation. Thermal analysis, X-ray diffraction and scanning electron microscopy were used for these studies. It was found that SrCoO3 forms at 930oC but is not stable and turn immediately into Sr2Co2O5 by eliminating of oxygen. This compound, Sr2Co2O5, is unstable and by increasing of the temperature decomposes in Sr3Co2O6 and cobalt oxide. At temperatures above the 1250oC, the samples melt and Sr3Co2O6 crystallizes from vitreous phase by cooling.

0.88Pb(Zr0.52Ti0.48)O3 – 0.12Pb(Mn1/3Sb2/3)O3 – 0,02 at%E piezoelectric ceramics, with E = Pr3+ were synthesized by using a conventional method, namely a solid state reaction technique. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) were employed for the structural and microstructural investigations. Piezoelectric methods were used for the dielectric and piezoelectric properties determination. The results of XRD show a perovskite structure and XRD patterns, indexing on a tetragonal cell structure, was carried out for the most common phases. The SEM micrographs of the sintered compositions reveal a homogenous structure with a sharp or rounded grain boundary. The modified PZT ceramic presents still superior piezoelectric properties. Based on the results obtained, one can conclude that the analysed piezoelectric ceramics are useful for device applications.

The magnetic and dielectric behavior of Portland cement mortars with various fly ashes (waste from the thermoelectric power plant) with a Fe2O3 content of 13.8 % was studied. The dielectric losses, tgd, the real component of the dielectric permeability, e�,and the real magnet permeability, �, the parameters with which we calculated the shielding coefficients, a, of the investigated samples, have been determined for the purpose of determining the screening capacity of the investigated samples by magnetic and dielectric spectroscopy in the 50 Hz � 3 kHz (ELF) range. Following experimental data processing, it was found that by increasing the hematite microstructured hematite Fe2O3 content of mortar samples (by fly ash addition) increased shielding capacity in the ELF domain, recorded increases for shielding coefficients, a, to an addition of up to 40 % fly ash, being up to 14.5 times at 50 Hz and up to 21 times at 3 kHz.

The influence of fly ash adittion (90 % fraction [ 100 mm) on the cement mortar characteristics was studied. The XRD, XRF, SEM and FTIR determinations indicated that fly ash used has a hollow microstructure of microsphere and cenosphere whose total content in SiO2, Al2O3 and Fe2O3 is 88.63 % and that of CaO and MgO of 8.55 %. The mechanical, thermal and dielectric determinations made on mortar samples with content of fly ash in the 0-40 % range have highlighted fact that the mechanical strength of cement mortars is maximal at 20 %, the increase in fly ash content leads to a decrease in relative density and thermal conductivity as well as and to increased dielectric losses tgd.

In this work it was studying evolution of the reactions that occur at the formation of La1-xSrxCoO3-� from mixtures of La2O3, Co3O4 and SrCoO3, prepared by mechanical activation. It was found that distributions of the particles sizes after mechanical activation are unimodal and narrow. Thermal analysis shows that the reactions that occur under the temperature of 1000oC are dissociation reactions of the raw materials or of intermediate compounds formed in the process of mechanical activation. The first compound found, starting from 1000oC was LaCoO3, whereas Co3O4 and CoO were observed as secondary phases. By measuring the apparent density of the thermally treated samples, a good tendency to sintering was noticed. SEM images and EDX analyses allowed to highlight the high sinterability of the samples.

High density graphite disks and aluminum nitride ceramics powders have been utilized to obtain joints by Spark Plasma Sintering technique. The joining was carried out in vacuum, at temperatures of 1700°C, 1800°C and 1900°C, under the pressure of 50 MPa with a constant dwelling time of 5 minutes The AlN ceramics to be joined were also synthesized by ceramic technology standard route by using AlN powders and 2.5 % wt.Y2O3 powders as sintering additive, which were added in order to increase densification rate and by thus, thermal conductivity. The joining of AlN/C was performed both without and with the aid of a ceramic powder composite AlN+Y2O3+C film, as interlayer. Besides the crystalline phases (AlN and C), the Al5Y3O12 compounds with a cubic crystallographic structure were identified by X-ray diffraction. The optical microscopy images revealed that all samples, both without and with film as interlayer, had strong joined areas, without any defects and discontinuities at interfaces. The Vickers microhardness and Young Modulus values measured by nanoindentation have shown that using of the film as intermediary layer was leading to the highest values of mechanical properties (HV = 8 – 23 GPa and E= 227-512 GPa) at the AlN/C joints interfaces.

The paper reports the effect of mechanical activation of La2O3 and Co3O4, the precursors for obtaining LaCoO3. The precursors were mechanically activated in a Fritsch Pulverisette 5 planetary mill for different durations (150 rpm). The optimal mechanical activation duration of the precursor powder is 10 h. The grain size distribution of the precursor powder at different grinding times was determined. The morphology of the powder was examined by scanning electron microscopy. Analysis by X-ray diffraction revealed that, for the synthesis of LaCoO3 to take place, grinding alone is not enough, subsequent thermal treatment being crucial. The transformation of the mix in terms of its physical and chemical characteristics was carried out by thermal analysis. At the 10 h mechanical activation, the formation of LaCoO3 was found to be fully completed at 1200 °C. However, at longer grinding times the reaction is fully completed only at 1250 °C.

ZnO based surge protective devices have been made and characterized both morphological (SEM microscopy and interferometry) and electrical (U/I characteristic and dielectric spectroscopy). SEM microscopy analyzes revealed that the disks of metal oxides sintered at 12000C present a homogeneous distribution of ZnO grains, without pores and well-defined intergranular limits. It was also found that Ag electrodes (applied by Ag paste to 650°C) are well anchored in the structure of the sintered material. The interferometry measurements revealed that the sintered material surface roughness ranges within ± 3μm. The electrical measurements revealed that the threshold voltage of the achieved devices is proportional to the thickness of the disks of approximately 156V / mm. Reverse currents, measured at 0.8 of the threshold voltage were between 0.28 and 0.31mA. Also, the measurements of dielectric spectroscopy revealed that the dielectric loss is highly dependent on frequency, respectively about 0.15 at 40 Hz and decreases exponentially to 0.019 at 10 kHz.