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Large energy storage density and high efficiency in Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramic induced by AgNbO3 doping.

25 h exhibited a giant dielectric constant (1.10 3 10 4 ) and a relatively low dielectric loss (0.033) around room temperature. The samples showed good temperature stability (DC T =C 25 C ¼ À6:7% -9.5%) in the temperature range from À60°C to 125°C at 10 kHz. It was also found that a new dielectric relaxation III appeared at higher temperatures (>200°C). The complex impedance spectroscopy analysis suggested that Y 2/3 Cu 3 Ti 4 O 12 ceramics were electrically heterogeneous, and they consisted of semiconducting grains and insulating grain boundaries, which could be modeled to a first approximation on an equivalent circuit based on two parallel RC elements connected in series. The Cu 2+ /Cu 3+ and Ti 3+ / Ti 4+ aliovalences were observed in Y 2/3 Cu 3 Ti 4 O 12 ceramics. The giant permittivity phenomenon could be explained by internal barrier layer capacitance (IBLC) effect.X. M. Chen-contributing editor Manuscript No. 30429.

Time crystals are physical systems whose time translation symmetry is spontaneously broken. Although the spontaneous breaking of continuous time-translation symmetry in static systems is proved impossible for the equilibrium state, the discrete time-translation symmetry in periodically driven (Floquet) systems is allowed to be spontaneously broken, resulting in the so-called Floquet or discrete time crystals. While most works so far searching for time crystals focus on the symmetry breaking process and the possible stabilising mechanisms, the many-body physics from the interplay of symmetry-broken states, which we call the condensed matter physics in time crystals, is not fully explored yet. This review aims to summarise the very preliminary results in this new research field with an analogous structure of condensed matter theory in solids. The whole theory is built on a hidden symmetry in time crystals, i.e., the phase space lattice symmetry, which allows us to develop the band theory, topology and strongly correlated models in phase space lattice. In the end, we outline the possible topics and directions for the future research.

The polymorphic structure evolution of (Ba,Ca)(Zr,Ti)O3 piezoelectric ceramics was investigated by analysis of the in situ X-ray diffraction and dielectric spectra. The results indicated that a confined orthorhombic (O) phase region induced by the approach of the rhombohedral (R) and tetragonal (T) phases existed in an extremely narrow temperature range of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 composition. The electric properties near the O–T phase boundaries of (Ba0.95Ca0.05)(Zr0.05Ti0.95)O3 and (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 were compared. The results suggested that the confined O phase region is an important factor that contributes to the extremely large piezoelectric response.

Hamiltonians which are inaccessible in static systems can be engineered in periodically driven manybody systems, i.e., Floquet many-body systems. We propose to use interacting particles in a onedimensional (1D) harmonic potential with periodic kicking to investigate two-dimensional topological and many-body physics. Depending on the driving parameters, the Floquet Hamiltonian of single kicked harmonic oscillator has various lattice structures in phase space. The noncommutative geometry of phase space gives rise to the topology of the system. We investigate the effective interactions of particles in phase space and find that the point-like contact interaction in quasi-1D real space becomes a long-rang Coulomb-like interaction in phase space, while the hardcore interaction in pure-1D real space becomes a confinement quark-like potential in phase space. We also find that the Floquet exchange interaction does not disappear even in the classical limit, and can be viewed as an effective long-range spin-spin interaction induced by collision. Our proposal may provide platforms to explore new physics and exotic phases by Floquet many-body engineering.

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