A cross-platform program, VESTA, has been developed to visualize both structural and volumetric data in multiple windows with tabs. VESTA represents crystal structures by ball-and-stick, space-filling, polyhedral, wireframe, stick, dot-surface and thermal-ellipsoid models. A variety of crystal-chemical information is extractable from fractional coordinates, occupancies and oxidation states of sites. Volumetric data such as electron and nuclear densities, Patterson functions, and wavefunctions are displayed as isosurfaces, bird's-eye views and two-dimensional maps. Isosurfaces can be colored according to other physical quantities. Translucent isosurfaces and/or slices can be overlapped with a structural model. Collaboration with external programs enables the user to locate bonds and bond angles in the `graphics area', simulate powder diffraction patterns, and calculate site potentials and Madelung energies. Electron densities determined experimentally are convertible into their Laplacians and electronic energy densities.

VESTA: a three-dimensional visualization system for electronic and structural analysis

Statistical physics has proven to be a fruitful framework to describe phenomena outside the realm of traditional physics. Recent years have witnessed an attempt by physicists to study collective phenomena emerging from the interactions of individuals as elementary units in social structures. A wide list of topics are reviewed ranging from opinion and cultural and language dynamics to crowd behavior, hierarchy formation, human dynamics, and social spreading. The connections between these problems and other, more traditional, topics of statistical physics are highlighted. Comparison of model results with empirical data from social systems are also emphasized.

Statistical physics of social dynamics

Since the subject of traffic dynamics has captured the interest of physicists, many surprising effects have been revealed and explained. Some of the questions now understood are the following: Why are vehicles sometimes stopped by ``phantom traffic jams'' even though drivers all like to drive fast? What are the mechanisms behind stop-and-go traffic? Why are there several different kinds of congestion, and how are they related? Why do most traffic jams occur considerably before the road capacity is reached? Can a temporary reduction in the volume of traffic cause a lasting traffic jam? Under which conditions can speed limits speed up traffic? Why do pedestrians moving in opposite directions normally organize into lanes, while similar systems ``freeze by heating''? All of these questions have been answered by applying and extending methods from statistical physics and nonlinear dynamics to self-driven many-particle systems. This article considers the empirical data and then reviews the main approaches to modeling pedestrian and vehicle traffic. These include microscopic (particle-based), mesoscopic (gas-kinetic), and macroscopic (fluid-dynamic) models. Attention is also paid to the formulation of a micro-macro link, to aspects of universality, and to other unifying concepts, such as a general modeling framework for self-driven many-particle systems, including spin systems. While the primary focus is upon vehicle and pedestrian traffic, applications to biological or socio-economic systems such as bacterial colonies, flocks of birds, panics, and stock market dynamics are touched upon as well.

Traffic and related self-driven many-particle systems

A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

Statistical physics of vehicular traffic and some related systems

Temperature dependences of the dielectric susceptibility, strain, piezoelectric constant, electrostrictive constant and elastic compliance in a two-sublattice model have been investigated by numerical calculations. The thermodynamic function in this model contains an asymmetric term W0 (P1 - P2) with respect to the sublattice polarizations P1 and P2. It has been shown that this term is an origin of unusual behaviors of piezoelectric and elastic properties. These results are applicable to the phase transitions and physical properties observed in Ca2Sr(C2H5CO2)6 (DSP) and Ca2Pb(C2H5CO2)6 (DLP).

Piezoelectric and elastic properties in a two-sublattice model

The Raman spectra of the relaxor ferroelectrics in the single crystals PbMg 1/3 Nb 2/3 O3(PMN), PbMg1/3Ta2/3O 3 (PMT), PbZnl/3Nb2/3O3(PZN) and PbNi1/3Nb2/3O 3 (PNN) have been measured in the frequency range up to 1000 cm −1 and in the temperature range between 100 K and 773 K. It was found that only in the PZN which exhibits the rhombohedral phase in the low temperature range, the spectra in the X(ZZ)Y and X(ZX)Y geometries are almost the same. We found that there are two modes at 50 cm−1 and 790 cm −1 in common in the all samples investigated

The Raman scattering in relaxor ferroelectrics

The Raman scattering spectra of C 6 H 5 NH 3 Br have been studied above and below the ferroelastic phase transition temperature T c =27°C. In contradiction with the previous inference based on X-ray diffuse scattering experiments that a transverse optical phonon as well as the transverse acoustic mode becomes unstable at the transition, no soft optical phonon was observed in the present Raman experiment.

Raman Scattering Study of Ferroelastic Phase Transition in C 6 H 5 NH 3 Br Crystal

The thermal dilatation in (NH3 ·CH3) SnCl6, (NH3 · C2H5) SnCl6 and [N(CH3)] SnCl6 was measured, and as the results it has turned out that (NH3 6·C2H5) SnCl6 and [N(CH3)4]2 SnCl6 undergo the first order transitions at 128 K and 158 K, respectively. The low temperature phases of (NH · C2H5) SnCl6 and [N(CH3)4]2 SnC16 are found to be monoclinic and tetragonal, respectively, No phase transition was observed in (NH3 ·CH3)2 SnCl6 down to 77 K.

Phase transitions in R2 SnCl6-type crystals (R = NH3 C2H3, NH3C2H5 and N(CH3)4)

The hydrostatic pressure–temperature ( P – T ) and Ca-concentration–temperature ( x – T ) phase diagrams of Ba 1- x Ca x TiO 3 (BCT) are discussed separately within the simple Landau–Devonshire theory. It is pointed out that it is not appropriate to discuss these phase diagrams under the assumption that physical factors governing the phase diagrams are the same. It is clarified that, in the P – T phase diagram, a decisive role is played by the effect in the second order in polarization, while in the x – T phase diagram, by that in the fourth order in polarization.

Yoshihiro Ishibashi

Papers

Piezoelectric and elastic properties in a two-sublattice model

The Raman scattering in relaxor ferroelectrics

Raman Scattering Study of Ferroelastic Phase Transition in C 6 H 5 NH 3 Br Crystal

Phase transitions in R2 SnCl6-type crystals (R = NH3 C2H3, NH3C2H5 and N(CH3)4)

Consideration on the Phase Diagrams of Ferroelectric (Ba,Ca)TiO3