Narrow Results

Front propagation in a random environment is studied close to the depinning threshold. At zero temperature we show that the depinning force distribution exhibits a universal behavior. This property is used to estimate the velocity of the front at very low temperature. We obtain a Arrhenius behavior with a prefactor depending on the temperature as a power law. These results are supported by numerical simulations.

Dynamics of a pinned dislocation kink controlled by the acting DC and AC forces is studied analytically. The motion of the kink, described by sine-Gordon (sG) equation, is explored within the framework of McLaughlin–Scott perturbation theory. Assuming weakness of the acting AC force, the equation of motion of the dislocation kink in the pinning potential is linearized. Based on the equations derived, we study stochastic behavior of the kink, and determine the probability of its depinning. The dependencies of the depinning probability on DC and AC forces are analyzed in detail.

Multiferroic 0.4 mol%-MnO₂-doped 0.78BiFeO₃–0.22BaTiO₃ ceramics were prepared by a traditional ceramic process. The effects of doping and annealing on the dielectric and ferroelectric properties were intensively investigated. Dielectric dispersion like relaxor ferroelectrics was observed in the oxygen annealed sample, but disappeared in the vacuum annealed sample. Modification of the BiFeO₃–BaTiO₃ with MnO₂ and annealing in vacuum improved DC resistivity obviously. The spontaneous polarization, remnant polarization, and coercive field are 65.2 μC/cm², 59.5 μC/cm² and 21.9 kV/cm, respectively under an applied field of 35 kV/cm.

High-performance lead-free piezoelectric materials are environmentally friendly and in great demand for electronic devices. In this study, the phase diagram and properties of Hf, Ca co-doped BaTiO₃ (BHT-BCT) were investigated. A triple-point morphotropic phase boundary separating the rhombohedral, tetragonal and cubic phases for the (1-$x$)Ba(Ti_0.85Hf_0.15)O₃-$x$(Ba_0.7Ca_0.3)TiO₃ system exited at $x=0.3.$ High piezoelectric properties with piezoelectric coefficients $d_{33}$ (572pC/N) and Curie temperature $T_c$ (90^∘C) of 0.55Ba(Ti_0.85Hf_0.15)O₃-0.45(Ba_0.7Ca_0.3)TiO₃ are achieved in the BaTiO₃-based ceramics.

We studied the statics and dynamics of elastic manifolds in disordered media with long-range correlated disorder using functional renormalization group (FRG). We identified different universality classes and computed the critical exponents and universal amplitudes describing geometric and velocity-force characteristics. In contrast to uncorrelated disorder, the statistical tilt symmetry is broken resulting in a nontrivial response to a transverse tilting force. For instance, the vortex lattice in disordered superconductors shows a new glass phase whose properties interpolate between those of the Bragg and Bose glasses formed by pointlike and columnar disorder, respectively. Whereas there is no response in the Bose glass phase (transverse Meissner effect), the standard linear response expected in the Bragg glass gets modified to a power law response in the presence of disorder correlations. We also studied the long distance properties of the O(N) spin system with random fields and random anisotropies correlated as 1/x^d-σ. Using FRG we obtained the phase diagram in (d, σ, N)-parameter space and computed the corresponding critical exponents. We found that below the lower critical dimension 4 + σ, there can exist two different types of quasi-long-range-order with zero order-parameter but infinite correlation length.