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International audience; The investigation of the phase transition sequence in SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN) is reported using single-crystal X-ray diffraction. By monitoring specific reflections as a function of temperature, sensitive either to the superstructure formation or to polar displacements, it was possible to check the existence or not of an intermediate phase. This latter was confirmed in SBT, but within experimental accuracy could not be detected in SBN.

Lead-free potassium sodium niobate (K0.5Na0.5)NbO3 thin films on Pt(111)/TiO2/SiO2/Si substrates have been prepared from the acetate–alkoxide-based precursor solutions with the stoichiometric composition and with 5 or 10 mol% excess of sodium or potassium acetate. Upon heating to 750°C, the films crystallize in pure perovskite phase. The increasing amount of alkali excess in solutions increases the degree of {100} orientation and it influences the nucleation and growth processes in the films. The microstructure of about 250 nm thick films prepared from the stoichiometric and 5 mol% excess solutions consists of equiaxed grains of about 50 nm across, whereas the grain size in the about 220 nm thick films prepared from the 10 mol% excess solutions is about 200 nm. The energy dispersive X-ray spectroscopy revealed that the alkali excess in precursor solutions contributed to a higher level of chemical homogeneity of the films on the micrometer scale. The chemical composition of the films prepared from the 5% potassium-excess solution was closest to the (K0.5Na0.5)NbO3 composition among all the samples as a result of more pronounced potassium losses upon heating. These films had the room temperature values of dielectric permittivity, dielectric losses, remnant polarization, and coercive field measured at 1 kHz 610, 0.015, 8 μC/cm2, and 80 kV/cm, respectively.

In this work, the effect of introducing tetragonal yttria-stabilized zirconia (TZ) particles in soft [Pb0.98Ba0.01][(Zr0.53Ti0.47)(0.98)Nb-0.02]O-3 (PZT) was investigated. Both microstructure and electrical properties of the PZT-xTZ (x = 0, 2, 5, 10, 20 vol%) composites were studied and correlated. The addition of zirconia hinders the matrix grain growth, resulting in smaller grains. According to X-ray diffraction analysis, zirconia containing composites have a higher rhombohedral-to-tetragonal phase ratio, in addition to lower dielectric and piezoelectric properties, in comparison to pure PZT. Electrical properties, in terms of strain- and polarization-electric field hysteresis curves, are presented and correlated with the observed phase compositions and microstructures. The extrinsic contribution to the piezoelectric properties in PZT and PZT-xTZ was studied by measuring the frequency and the stress field amplitude dependences of the piezoelectric d(33) coefficient.

In2O3–ZnO two-dimensional (2D) structures were processed by ink-jet printing and heating at 150°C and 450°C with the aim for implementation in transparent electronics. The In–Zn-solution precursor, based on In-alkoxide and Zn-acetate in 2-methoxyethanol, was originally designed for chemical solution deposition of thin films. To adapt it for piezoelectric ink-jet printing, the viscosity and surface tension were adjusted by the addition of a more viscous 1,3-propanediol. The optimum values were obtained for the ink consisting of 55 vol% of 1,3-propanediol. The printing parameters including the temperatures of the cartridge and the substrate, and the drop spacing were adjusted to allow patterning with a 40 μm resolution on SiOx/Si and glass substrates. The ink-jet-printed 2D structures heated at 150°C were amorphous and according to infrared spectroscopy organics-free, and upon heating at 450°C they crystallized without any preferential orientation, similarly as the spin-coated thin films, which were studied as a reference.

In this review, the crystal structure and the synthesis of the sodium potassium niobate ( K 0.5 Na 0.5 NbO 3) as a promising candidate for lead-free piezoelectrics are addressed. The sintering and the microstructure as prerequisites for obtaining ceramics with reliable and sufficiently high piezoelectric properties for selected applications are discussed.

This paper presents the crystal structure and the phase transitions of K x Na 1− x NbO 3 (0.4 ≤ x ≤ 0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100–800 K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° ≤ β ≤ 90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic–tetragonal and tetragonal–cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K.

The room temperature structures of the four-layer Aurivillius phase ferroelectrics CaBi4Ti4O15 and BaBi4Ti4O15 are determined by means of single crystal X-ray diffraction. Regarding the CaBi4Ti4O15 phase, in agreement with the tolerance factor, a significant deformation of the perovskite blocks is observed. The rotation system of the octahedra is typical from even layer Aurivillius phases and leads to the use of the space group A21am. For the BaBi4Ti4O15 phase, only a weak variation with respect to the F2mm space group can be suggested from single crystal X-ray diffraction. A significant presence of Ba atoms in the [M2O2] slabs is confirmed in agreement with the previous works but specific Ba2+ and Bi3+ sites have to be considered due to the large difference in bounding requirement of these cations. Possible origins for the ferroelectric relaxor behavior of the Ba-based compound are discussed in view of the presented structural analyses.

In this investigation we show that the dielectric, ferroelectric and piezoelectric properties of stoichiometric 0.57Pb(Sc 1/2 Nb 1/2 )O 3 –0.43PbTiO 3 (0.57PSN–0.43PT) ceramics prepared by mechanochemical synthesis are comparable or even better than the properties of 0.57PSN–0.43PT ceramics with Nb doping, which was proposed to enhance the electrical properties. Here, the stoichiometric ceramic was sintered to 97% of theoretical density at a temperature of 1000 °C, which is 200–300 °C lower than previously reported. The dielectric constant ɛ , remnant polarization P r , piezoelectric coefficient d 33 , coupling coefficients k p and k t and mechanical quality factor Q m of the ceramics prepared by mechanochemical synthesis were 2200, 43 μC/cm 2 , 570 pC/N, 0.71, 0.56 and 38, respectively. The effects of the poling field on the structural and electrical properties of the 0.57PSN–0.43PT ceramics were investigated. The results show that the ratio of the monoclinic to the tetragonal phases is influenced by the application of the poling electric field. The non-poled ceramics contain 71% of the monoclinic phase and 29% of the tetragonal phase. The highest d 33 , k p and k t were measured for ceramics poled at an electric field of 3 kV/mm. For these poled ceramics a phase determination of 86% monoclinic phase and 14% tetragonal phase was obtained from Rietveld refinements.

International audience; Thick films with the nominal composition 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) (0.65PMN-0.35PT) were produced by screen-printing and firing paste prepared from an organic vehicle and pre-reacted powder. The films were fired for 2 h at 950 degrees C on alumina (Al2O3), platinum (Pt), aluminium nitride (AlN) and 0.65PMN-0.35PT substrates. The films were then characterized using scanning electron microscopy, X-ray diffraction and dielectric constant measurements. The X-ray analysis did not detect the presence of any undesirable pyrochlore phase, and the differences in the phase compositions were determined with a Rietveld refinement. The variations of the cell parameters vs. the temperature for the monoclinic and tetragonal phases were calculated. It was demonstrated that under similar processing conditions the microstructures, phase compositions and dielectric properties strongly depended on the stress in the thick films due to the different temperature expansion coefficients of the thick films and the substrates. The 0.65PMN-0.35PT thick films under compressive stresses (for the case of the Al2O3 and Pt substrates) exhibited a tetragonal phase in addition to the monoclinic one. The films were sintered to a high density and with a coarse microstructure. These microstructures favour a high dielectric constant. In contrast, for the films under a tensile stress, like the films on AlN substrates, the films were sintered to a lower density and the microstructure consisted of smaller grains. The X-ray analysis showed mainly a monoclinic phase, while the tetragonal phase was not detected. These results indicate the importance of the stresses in 0.65PMN-0.35PT thick films and their influence on the structural and electrical characteristics of the films.

This paper presents the crystal structure and the phase transitions of K x Na 1− x NbO 3 (0.4 ≤ x ≤ 0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100–800 K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° ≤ β ≤ 90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic–tetragonal and tetragonal–cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K.

Two solid solutions of three-layer Ba x Bi 4− x Nb x Ti 3− x O 12 (0 ≤ x ≤ 1.2) and four-layer Aurivillius compounds (Na 0.5 Bi 0.5 ) 1− x Ba x Bi 4 Ti 4 O 15 (0 ≤ x ≤ 1), which both present a ferroelectric to relaxor-like transition with increasing x , were synthesized by solid state reaction. The evolution of their crystal structures, as a function of x , was performed using Rietveld refinements from X-ray powder diffraction data. As x increases, the average crystal structures become less distorted with respect to the archetypal high temperature tetragonal one and the coordination number of Bi 3+ in M 2 O 2 layers continuously changes from {4 + 2} to {4}. The relaxor behaviour which appears in samples for a tolerance factor t > 0.96 is associated with a general static disorder in A and M sites together with the presence of some Ba 2+ cations in M 2 O 2 layers (less than 10%).

The crystal structure of four Aurivillius phases within the pseudo-binary system Bi4Ti3O12—PbTiO3 is examined using a 3 + 1D approach where these phases are treated as commensurately modulated layered structures. The structure of PbBi4Ti4O15, Pb2Bi4Ti5O18, Pb3Bi4Ti6O21 and PbBi8Ti7O27 are refined by the Rietveld method using XRPD data from single phased powders. The structure of Pb3Bi4Ti6O21 and PbBi8Ti7O27 is reported for the first time. When the lead content increases, the structure gets less distorted and approaches the prototype paraelectric phase in an apparent close relation with the onset of a “relaxor-like” ferroelectric behaviour. For these relaxor compounds, SAED investigation evidences the existence of a disorder in the form of micro-twinning.

Structure refinements in M II Bi 4 Ti 4 O 15 (M II = Ca, Ba), Bi 4− x Ba x Ti 3− x Nb x O 12 , (Na 0.5 Bi 0.5 ) 1− x Ba x Bi 4 Ti 4 O 15 and Bi 4 Ti 3 O 12 –PbTiO 3 systems are used to report structural features of relaxor Aurivillius phases. In compounds with relaxor-like behaviour, the average structure is almost undistorted, closed to the archetypal HT paraelectric phase, with a tolerance factor ≳0.996. The coordination number of Bi 3+ in fluorite layers changes from {4 + 2} for ferroelectrics to {4} for relaxors. Transmission Electron Microscopy reveals some characteristic features of relaxors such as micro-twinning, shearing-type defects which attest from the existence of a compositional inhomogeneity and a disorder at a local scale.

The crystal structure of the 1 + 2 mixed-layer Aurivillius phase Bi5Ti1.5W1.5O15 (SG I2cm no 46: − c b a , Z = 4 , a = 5.4092 ( 3 ) A , b = 5.3843 ( 3 ) A and c = 41.529 ( 3 ) A ) consisting of the ordered intergrowth of one and two octahedra thick perovskite-type blocks separated by [Bi2O2]2+ slabs is reported. Supported by an electron diffraction investigation and, using the Rietveld analysis, it is shown that this compound should be described using a I-centering lattice in agreement with the generalised structural model of the Aurivillius type compounds recently presented by the authors. The structure of this Bi5Ti1.5W1.5O15 phase is analyzed in comparison with the related simple members (Bi2WO6 and Bi3Ti1.5W0.5O9). The crystal structure of Bi3Ti1.5W0.5O9 is also reported.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

The effects of the poling field on the structural and electrical properties of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.65PMN–0.35PT) ceramics were investigated. The highest piezoelectric coefficient d 33, coupling coefficients k p, k t, and mechanical quality factor Q m were achieved for ceramics poled at electric fields between 2 and 3.5 kV/mm, whereas the d 33, k p, k t, and Q m of ceramics poled at higher electric fields, i.e., 4 and 4.5 kV/mm, were lower. The non-poled ceramics contained 86% of the monoclinic phase with the space group P m and 14% of the tetragonal phase with the space group P4m m. However, the ceramics poled at 2.5 kV/mm contained 99% of the monoclinic phase and the rest is the tetragonal phase. The results show that the ratio of the monoclinic to the tetragonal phases can be changed by the application of a poling electric field and that the extent of this change is dependent on the field strength.

The influence of thermal stresses versus the phase composition for 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.65PMN–0.35PT) thick films is being reported. The thermal residual stresses in the films have been calculated using the finite-element method. It has been observed that in 0.65PMN–0.35PT films a compressive stress enhances the thermodynamic stability of the tetragonal phase with the space group P4mm.

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 °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 °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...

Following an x-ray diffraction study of phase transitions of the piezoelectric perovskite K0.5Na0.5NbO3 the structural changes of the material are studied using extended x-ray absorption fine structure analysis, whereby the neighborhood of Nb atom is determined in the temperature range of monoclinic, tetragonal, and cubic phases. Within the entire range Nb atom is displaced from the center of the octahedron of its immediate oxygen neighbors, as witnessed by the splitting of Nb–O distance. The model shows high prevalence of the displacement in the (111) crystallographic direction of the simple perovskite cell. The corresponding splitting of the Nb–Nb distance is negligible. There is no observable disalignment of the linear Nb–O–Nb bonds from the ideal cubic arrangement, judging from the intensity of the focusing of the photoelectron wave on the Nb–Nb scattering path by the interposed oxygen atom. As a general result, the phase transitions are found as an effect of the long-range order, while the placement ...