M. Pawełczyk

Diffuse phase transitions in Pb(Zr, Ti)O3 solid solutions with up to 3 % Ti content

Abstract Using X-rays the volume content of neighbouring phases and the temperature variation of unit cell volume have been investigated in the vicinity of phase transitions between the para-, ferro-and antiferroelectric states for Pb(Zr, Ti)O3 ceramic with Ti content up to 3%. The diffuse nature of the phase transitions has been confirmed in the solid solutions.

Phase composition and dielectric properties of lead barium zirconate solid solutions

Abstract Results are presented of X-ray analysis and also dielectric and pyroelectric studies on (Pb1−x Ba x )ZrO3 (x ≤ 0.25) solid solutions. The coexistence of A, F and P phases in the vicinity of phase transition temperatures was determined and correlation between phase composition of samples with various Ba content and the form of spontaneous polarization versus dopant concentration function was established. It was also ascertained that on the both sides of transient ferroelectric phase there exist ferroelectric microdomains responsible for ferroelectric relaxor type behavior of (Pb1-x Ba x )ZrO3 solid solutions and that Ba content markedly influences these properties.

Resistance Switching Induced in BiMnO3 Ceramics

In our study BiMnO3 ceramics has been sintered. The X-ray diffraction test has shown that the crystal lattice symmetry is monoclinic and centrosymmetric. Grain structure and stoichiometry has been determined by scanning electron microscopy whereas local disorder by X-ray photoemission spectroscopy. Leakage currents dominated the D–E hysteresis loop. Electric conductivity has been measured in the 85–770 K range. The studied fresh ceramics shows semiconductor properties. Charge-order transition occurrence has been deduced. The dc resistance switching occurs following the application of electroformation at a high temperature range. This effect is reversible, i.e. the Rdc(T) recovers semiconductor properties after thermal and electric field treatment.

Phase transitions in lead-lanthanum zirconate-titanate ceramics with a Zr/Ti ratio of 92/8 and a La content of up to 1 at.%

Phase transitions and phase sequence in La-doped lead zirconate-titanate ceramics with a Zr/Ti ratio of 92/8 and La content up to 1 at.% were investigated by dielectric, pyroelectric, X-ray and Raman scattering methods. The phase sequence antiferroelectric (A0)-low-temperature ferroelectric (FR(LT))-high-temperature ferroelectric (FR(HT))-paraelectric (pc) was confirmed in these ceramics. The results obtained indicate the need to ascertain a precise phase diagram of PLZT materials in the range close to the phase boundary separating the A0 and FR phases for low lanthanum contents by taking into account the occurrence of both FR(LT) and FR(HT) phases.

Chemical inhomogeneity in the near-surface region of KTaO3 evolving at elevated temperatures

Measurements by x-ray diffraction, secondary ion mass spectrometry and atomic force microscopy are reported for single crystalline KTaO3 after thermal treatment under oxidizing conditions in the temperature range of 700 to 1100 °C. The formation of a series of new phases KO*(KTaO3)n of Ruddlesden-Popper type is observed. Atomic force microscopy of (100) surfaces reveals corresponding dramatic changes in the surface morphology. Secondary ion mass spectrometry gives evidence of a redistribution of material leading to an enrichment of K with respect to Ta close to the surface and a corresponding depletion in deeper parts of the near-surface region. The results are in strong contrast to standard point defect models. Instead, our experimental observations have to be interpreted in terms of an evolving chemical inhomogeneity due to segregation processes in the near-surface region of the crystals and intergrowth of KO, which results in the formation of the Ruddlesden-Popper phases. The additional effect of K2O evaporation above 900 °C is discussed and the corresponding topographical changes induced are documented.

Changes in structure and electrical properties of NaNbO3 induced by Mn dopant

The electric permittivity of ceramic NaNbO3: x Mn (x=0-1 wt.%) was measured in the range 20-500 degrees C. The Mn dopant induces an additional anomaly in the epsilon (T). The temperature of the maxima in epsilon (T) is shifted under applied axial pressure. The X-ray test proved that the anomalies in epsilon (T) are related to the structural phase transitions.

Investigation of the structure, pyro- and piezoelectric properties of a ferroelectric ceramic of PZT+(fesb)

Abstract X - ray diffraction studies of polycrystalline Pb[(Fe 1/3 Sb 2/3) xTiy Zrz ]O 3 with x + y + z = 1, x = 0.1 and y = 0.43 – 0.47 have been performed in the temperature range between 23°C to 380°C. The results indicate that below 220°C rhombohedral and tetragonal phases coexist; above 220°C the cubic symmetry phase only. The amount of the rhombohedral phase decrease with increasing temperature for all values of y. The pseudo perovskite cell parameters and their temperature dependence were determined. The pyrocurrents in the temperature range from 25°C to 380°C were measured.

On the Pb thermal vibrations in PbHfO3 crystals

In PbHfO3 single crystals the amplitude of the thermal vibrations for Pb ions in the high-temperature Pm3m phase, calculated from the Debye-Waller factor, reached unexpectedly large values. The random displacements of Pb ions were assumed and the new thermal vibration amplitude, which is more reasonable from the crystal lattice dynamics point of view, was calculated. A possible displacive-type phase transition was observed in the vicinity of 400 degrees C.

Structure and electrical properties of PbZrO3 doped with Nb2O5

Results are presented of complex studies on the structural, dielectric and pyroelectric properties and also on the electrical conductivity and Seebeck effect in samples of ceramic PbZrO3 + x Nb2O5 (where 0 < x ≤ 2% mol). Marked variations in these properties were observed when the concentration of Nb2O5 became greater than 1.2% mol. It was ascertained that this is connected with the creation of a large number of vacancies in the Pb sublattice.

The antiferroelectric-ferroelectric-paraelectric phase sequence in lead-lanthanum zirconate-titanate ceramics with 8% Ti content

Phase transitions in PLZT 2/92/8 ceramics were investigated by X-ray, dielectric, pyroelectric and Raman scattering measurements. The antiferroelectric-ferroelectric-paraelectric phase sequence in this material was confirmed. The antiferroelectric and ferroelectric phases coexist in an exceptionally wide low-temperature range. Possible reasons for the differentiation in properties of the ferroelectric phase in the high- and low-temperature ranges are discussed.