S. B. Vakhrushev

Glassy phenomena in disordered perovskite-like crystals

Abstract Peculiarities of phase transitions in disordered perovskite-like crystals—PbMg1/3 Nb2/3 O3 (PMN) and Na1/2 Bi1/2 TiO3 (NBT) have been studied by neutron scattering. The strong quasielastic scattering (QES) related to ferroelectric critical fluctuations has been observed instead of expected inelastic scattering of soft phonon mode. The wavevector dependence of this diffuse scattering has been well described by Ornstein-Zernice formula. The correlation length temperature dependence resembling that of spin-glasses has obtained. The history dependent effects have been found by measurements in electric field in “field cooled” (FC) and “zero field cooled” regimes. Those effects as well as long-time relaxation of Bragg peaks intensity, observed below certain temperature, clearly indicate glass-like nature of low-temperature phase.

The rhombohedral phase with incommensurate modulation in Na1/2Bi1/2TiO3

The phase transition from tetragonal to rhombohedral phase in sodium bismuth titanate (NBT) is studied by means of neutron scattering. It is found that the rhombohedral phase has incommensurate modulation along the four-fold axis of the precursor tetragonal phase. The appearance of the incommensurate modulation is discussed on the symmetry grounds in the framework of the phenomenological theory of phase transitions.

Ferroelectric phase transitions in materials embedded in porous media

Abstract Large quantities of highly dispersed ferroelectric objects were obtained by impregnation of two porous dielectric matrixes (porous glass and artificial opal) with molten ferroelectric materials (NaNO2, KH2PO4 (KDP)). The diameters of ferroelectric nanoparticles may be varied from about 100 nm to 3–4 nm. The neutron scattering measurements for NaNO2 particles and low frequency dielectric permittivity measurements for NaNO2, KDP and Rochelle salt particles were performed on such nanosize particles systems. The significant shift of transition temperature from the bulk value for KDP particles as the transition broadening for NaNO2 and KDP particles was observed.

Field induced kinetic ferroelectric phase transition in lead magnoniobate

Abstract The time dependence of the complex dielectric permittivity of lead magnoniobate (PMN) single crystal in an applied external DC field, was studied. The field was applied in a “zero-field-cooling” regime. All measurements were carried out for the low-temperature PMN non-ergodic glassy phase. The transition to the polar state at a time τ from the moment of field application was observed. The dependence of τ on both temperature and applied field was obtained

Structure of KD 2 PO 4 Embedded in a Porous Glass

The temperature evolution of the crystal structure of KD 2 PO 4 (DKDP) embedded in a porous glass with 7 nm pore diameter has been studied by neutron diffraction in temperature interval 90 K-308 K. It is shown that confined DKDP forms interconnected clusters with characteristic size of 18(0.5) nm. The structure of this nanocomposite material is found to be monoclinic and corresponds to the space group P 2 1 . The lattice parameters and characteristic cluster size are temperature independent and do not reveal any peculiarities in the vicinity of expected ferroelectric phase transition of 223 K.

The Technique of Studying X-Ray Scattering over Wide Temperature Range in an Electric Field

The technique of studying the synchrotron radiation scattering on single crystals over wide temperature range using an original miniature device for applying an electric field to a sample is described. A specific feature of the device is the possibility of its application with various heating and cooling systems. The technique was used at BM01 beamline at the European Synchrotron Radiation Facility (ESRF) for the study of the influence of electric field on the processes of structural transformation in lead zirconate–titanate single crystal with a low titanium concentration. The efficiency of the technique proposed in this work is demonstrated and the results of the preliminary analysis of the results are presented.

Domain structures and correlated out-of-plane and in-plane polarization reorientations in Pb(Zr0.96Ti0.04)O3 single crystal via piezoresponse force microscopy

Pb(Zr1-xTix)O3 single crystal with a low titanium content (x = 4%) was studied by the piezoresponse force microscopy (PFM) and X-ray diffraction (XRD). The XRD studies showed that the crystal faces are orthogonal to the principal cubic axes and confirmed the existence of an intermediate phase between the high-temperature paraelectric (PE) phase and the low-temperature antiferroelectric (AFE) one. A significant temperature hysteresis of phase transitions was observed by the XRD: On heating, the AFE state transforms into the intermediate one at about 373 K and the PE phase appears at 508 K, whereas on cooling the intermediate phase forms at 503 K and persists down to at least 313 K. The PFM investigation was focused on the intermediate phase and involved measurements of both out-of-plane and in-plane electromechanical responses of the (001)-oriented crystal face. The PFM images revealed the presence of polarization patterns switchable by an applied electric field, which confirms the ferroelectric character ...

Low Temperature Ferroelectric and Magnetic Properties of Doped Multiferroic Tb0.95Bi0.05MnO3

Multiferroics are very promising materials for application in RF/microwave electronic devices. Electrical tuning of magnetism due to strong magnetoelectric coupling in these materials gives an opportunity to use them in reconfigurable microwave devices, ultra-low power electronics and magnetoelectric random access memories (MERAMs). Tb0.95Bi0.05MnO3 (TMNO) multiferroic is a solid solution of TbMnO3 and BiMnO3, the interest to investigation of this nanocomposite material is caused by the possibility to obtain the multiferroic with close temperatures of magnetic and ferroelectric ordering which are higher than in pure TbMnO3. Results of TMNO crystal investigations obtained using cryogenic magnetic force and piezopresponse force microscopy techniques are presented. An existence of ferroelectric and ferromagnetic ordering in TMNO at low temperatures was observed.

Temperature Dependence of Ferroelectric Properties of the Potassium Lithium Tantalate K1−xLixTaO3 Obtained with Piezoresponse Force Microscopy Technique

Abstract In the present paper we report the first results of the study of the polar state of the surface structure of single crystal of potassium tantalate doped with Li + ions (KLT-3%) by the piezoresponse force microscopy technique in the temperature range 10–295 K. The results obtained demonstrate the existence of polar nanoregions on the surface of the KLT-3% single crystal at temperatures 10 – 80 K. Spatial distribution and temperature evolution of these polar nanoregions are analyzed. Observation of the structure of polar nanoregions of KLT-3% crystal in zero field heating after zero field cooling regime gives the evidence of the existence of spontaneous polarization in the low-temperature phase.

X-Ray Scattering by Antiphase Ferroelectric Domain Walls in the Antiferroelectric Phase of the PbZr

The results of the X-ray diffuse scattering (DS) measurements of the Zr-rich PbZrO\(_{3}\) - PbTiO\(_{3}\) solid solution PbZr\(_{0.985}\)Ti\(_{0.015}\)O\(_3\) (PZT1.5) are presented. Measurements were performed in zero electric field and in applied electric field E = 5 kV / cm. In the antiferroelectric phase diffuse scattering streaks around \(\varSigma \) superstructure peaks \((h+\frac{1}{4}~k+\frac{1}{4}~l)\) were found and interpreted as a scattering on ferroelectric antiphase domain walls. This conclusion is corroborated by the observation of a strong influence of the electric field on these streaks. Reported results are important for the prospective application of the antiferroelectrics as the basis for the high-density non-volatile memory devices.