다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Relaxor ferroelectrics were discovered almost 50 years ago among the complex oxides with perovskite structure. In recent years this field of research has experienced a revival of interest. In this paper we review the progress achieved. We consider the crystal structure including quenched compositional disorder and polar nanoregions (PNR), the phase transitions including compositional order-disorder transition, transition to nonergodic (probably spherical cluster glass) state and to ferroelectric phase. We discuss the lattice dynamics and the peculiar (especially dielectric) relaxation in relaxors. Modern theoretical models for the mechanisms of PNR formation and freezing into nonergodic glassy state are also presented.

Recent progress in relaxor ferroelectrics with perovskite structure

After twenty years of partly quiet and ten years of partly enthusiastic research into lead-free piezoceramics there are now clear prospects for transfer into applications in some areas. This mimics prior research into eliminating lead from other technologies that resulted in restricted lead use in batteries and dwindling use in other applications. A figure of merit analysis for key devices is presented and used to contrast lead-containing and lead-free piezoceramics. A number of existing applications emerge, where the usage of lead-free piezoceramics may be envisaged in the near future. A sufficient transition period to ensure reliability, however, is required. The use of lead-free piezoceramics for demanding applications with high reliability, displacements and frequency as well as a wide temperature range appears to remain in the distant future. New devices are outlined, where the figure of merit suggests skipping lead-containing piezoceramics altogether. Suggestions for the next pertinent research requirements are provided.

Transferring lead-free piezoelectric ceramics into application

Due to the nature of domains, ferroics, including ferromagnetic, ferroelectric, and ferroelastic materials, exhibit hysteresis phenomena with respect to external driving fields (magnetic field, electric field, or stress). In principle, every ferroic material has its own hysteresis loop, like a fingerprint, which contains information related to its properties and structures. For ferroelectrics, many characteristic parameters, such as coercive field, spontaneous, and remnant polarizations can be directly extracted from the hysteresis loops. Furthermore, many impact factors, including the effect of materials (grain size and grain boundary, phase and phase boundary, doping, anisotropy, thickness), aging (with and without poling), and measurement conditions (applied field amplitude, fatigue, frequency, temperature, stress), can affect the hysteretic behaviors of the ferroelectrics. In this feature article, we will first give the background of the ferroic materials and multiferroics, with an emphasis on ferroelectrics. Then it is followed by an introduction of the characterizing techniques for the loops, including the polarization–electric field loops and strain–electric field curves. A caution is made to avoid misinterpretation of the loops due to the existence of conductivity. Based on their morphologic features, the hysteresis loops are categorized to four groups and the corresponding material usages are introduced. The impact factors on the hysteresis loops are discussed based on recent developments in ferroelectric and related materials. It is suggested that decoding the fingerprint of loops in ferroelectrics is feasible and the comprehension of the material properties and structures through the hysteresis loops is established.

Decoding the Fingerprint of Ferroelectric Loops: Comprehension of the Material Properties and Structures

Rietveld neutron powder profile analysis of the compound Na0.5Bi0.5TiO3 (NBT) is reported over the temperature range 5–873 K. The sequence of phase transitions from the high-temperature prototypic cubic structure (above 813 K), to one of tetragonal (673–773 K) and then rhombohedral structures (5–528 K) has been established. Coexisting tetragonal/cubic (773–813 K) and rhombohedral/tetragonal (with an upper temperature limit of 145 K between 528 and 673 K) phases have also been observed. Refinements have revealed that the rhombohedral phase, space group R3c, with aH = 5.4887 (2), cH = 13.5048 (8) A, V = 352.33 (3) A3, Z = 6 and Dx = 5.99 Mg m−3, exhibits an antiphase, a−a−a− oxygen tilt system, ω = 8.24 (4)°, with parallel cation displacements at room temperature. The tetragonal phase, space group P4bm, with aT = 5.5179 (2), cT = 3.9073 (2) A, V = 118.96 (1) A3, Z = 2 and Dx = 5.91 Mg m−3, possesses an unusual combination of in-phase, a0a0c+ oxygen octahedra tilts, ω = 3.06 (2)°, and antiparallel cation displacements along the polar axis. General trends of cation displacements and the various deviations of the octahedral network from the prototypic cubic perovskite structure have been established and their systematic behaviour with temperature is reported. An investigation of phase transition behaviour using second harmonic generation (SHG) to establish the centrosymmetric or non-centrosymmetric nature of the various phases is also reported.

Investigation of the structure and phase transitions in the novel A-site substituted distorted perovskite compound Na0.5Bi0.5TiO3

An x-ray diffraction study of the paraphase of the (PbMg1/3Nb2/3O3)0.6-(PbTiO3)0.4 solid solution has been found to exhibit a clearly pronounced ferroelectric transition. It is shown that Pb2+ ions occupy a special position (000), as opposed to pure PMN and other relaxor ferroelectrics, where they are displaced from it in random directions. The absence of these displacements indicates suppression of frozen-in random electric fields in this compound.

Unique features of the crystal structure of the (PbMg1/3Nb2/3O3)0.6-(PbTiO3)0.4 solid solution

The structure of the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 crystal was studied with the X-ray single crystal diffraction at 110, 224 and 293 K The remarkable redistribution of the reflections intensities at low temperatures was observed The structure of the low temperature phase is described with the model of the substantially nonuniform displacements of the lead ions using the derived analytical expression of the scattering form-factor The structure refinement shows the good agreement between the model and the experimental data at low temperatures

Structural study of Pb(Mg1/3Nb2/3)O3 at low temperatures

High energy resolution neutron spin-echo spectroscopy has been used to measure intrinsic width of diffuse scattering discovered earlier in relaxor ferroelectric crystals. The anisotropic and transverse components of the scattering have been observed in different Brillouin zones. Both components are found to be elastic within experimental accuracy of 1 eV. Possible physical origin of the static-like behavior is discussed for each diffuse scattering contribution.

Diffuse neutron scattering in relaxor ferroelectric PbMg1/3Nb2/3O3

An analysis of the high-temperature phase structure of multiferroic solid solutions of the PFW–PT

An experimental study of low temperature domain dynamics could provide information on a mechanism of domain wall motion at low temperatures in thin ferroelectric films. For this purpose we use a piezoresponse force microscopy (PFM) technique and investigate the 1800 ferroelectric domains growth in the temperature range 5 K – 295 K. Domains were created by applying a dc voltage pulses between an atomic force microscopy (AFM) tip and a bottom electrode of a thin epitaxial PbZr0.3Ti0.7O3 film. Two different types of tips were used, a semiconducting tip with dopant conductivity and a tip with metallic coating to clarify an influence of poling procedure on the domain dynamics. Created domains were then visualized and their in-plane sizes were measured with out-of-plane PFM. Dependences of lateral domain size on the duration and amplitude of dc voltage pulse were obtained. Received experimental dependences were then fitted with logarithmic function with good accuracy. This circumstance indicates on the thermally activated mechanism of domain growth and formation. Temperature dynamics of the 1800 ferroelectric domains growth does not depend on the AFM tip used in a poling procedure what allows us to conclude that the voltage transfer to the ferroelectric film does not significantly depend on the tip-film local contact properties.

Sergey Vakhrushev

Papers

Unique features of the crystal structure of the (PbMg1/3Nb2/3O3)0.6-(PbTiO3)0.4 solid solution

Structural study of Pb(Mg1/3Nb2/3)O3 at low temperatures

Diffuse neutron scattering in relaxor ferroelectric PbMg1/3Nb2/3O3

An analysis of the high-temperature phase structure of multiferroic solid solutions of the PFW–PT

Influence of a Poling Procedure on Dynamics of Ferroelectric Domains in Thin PbZr0.3Ti0.7O3 Film at Low Temperatures