Hybrid soft-mode and off-center Ti model of barium titanate

R. Pirc; R. Blinc

Home/Archive/arXiv

arXiv · cond-mat/0401081

Hybrid soft-mode and off-center Ti model of barium titanate

R. Pirc·R. Blinc

View original source ↗Read source document ↗Export metadata ↓

Abstract

It has been recently established by NMR techniques that in the high temperature cubic phase of BaTiO$_3$ the Ti ions are not confined to the high symmetry cubic sites, but rather occupy one of the eight off-center positions along the $[111]$ directions. The off-center Ti picture is in apparent contrast with most soft-mode type theoretical descriptions of this classical perovskite ferroelectric. Here we apply a mesoscopic model of BaTiO$_3$, assuming that the symmetrized occupation operators for the Ti off-center sites are linearly coupled to the normal coordinates for lattice vibrations. On the time scale of Ti intersite jumps, most phonon modes are fast and thus merely contribute to an effective static Ti-Ti interaction. Close to the stability limit for the soft TO optic modes, however, the phonon time scale becomes comparable to the relaxation time for the Ti occupational states of $T_{1u}$ symmetry, and a hybrid vibrational-orientational soft mode appears. The frequency of the hybrid soft mode is calculated as a function of temperature and coupling strength, and its its role in the ferroelectric phase transition is discussed.

Explore related subjects

cond-mat.stat-mech

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

R. Pirc, R. Blinc. 2004-01-07. Hybrid soft-mode and off-center Ti model of barium titanate. https://arxiv.org/abs/cond-mat/0401081

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Universal sampling of spin systems across quenched disorder

Statistical physics extracts macroscopic laws by averaging over the many microscopic degrees of freedom of a system. Disordered systems demand a second and far harder average, one over the quenched randomness itself. The classic analytical routes, the replica and cavity methods, become uncontrolled outside mean-field or tree-like limits, and conventional numerical algorithms like parallel tempering require expensive, independent equilibration for every disorder realization. In this work, we introduce a universal neural variational framework that amortizes inference across the disorder ensemble, eliminating both the need for per-instance Markov chain equilibration and the cost of retraining instance-specific variational ansatzes. Built on an encoder-decoder Transformer architecture, after training once, it produces an explicit approximation to the Boltzmann distribution given previously unseen disorder realizations without further optimization. We validate this framework on 2D Edwards-Anderson models, and apply it to the random-bond Ising model, successfully capturing the Binder cumulant crossings near the Nishimori multicritical point. These results shift the object of variational inference from the single instance to the disorder ensemble, opening a route to frustrated many-body systems where instance-by-instance computation is prohibitive.

cond-mat.stat-mech↗

arXiv2026

Information-Theoretic Characterization of Macroscopic Chaos Emerging from the Chemical Master Equation

Open chemical reaction networks exhibit stochastic concentration dynamics at finite system sizes, whereas their macroscopic limit is governed by deterministic rate equations that can display chaos. In this Letter, we show theoretically that a rate of information loss constructed from two-time mutual information recovers the Kolmogorov-Sinai entropy in the deterministic limit. We verify this result through numerical simulations of a Markov jump process for a three-species system involving seven reactions.

cond-mat.stat-mech↗

arXiv2026

Orientational order on non-orientable domains

We study the statistical properties of passive and active many-body systems with orientational degrees of freedom on non-orientable domains. By rephrasing topological constraints as non-local symmetry relations on an orientable double-cover, we show that non-orientability eliminates global rotational soft modes without acting like an external field. In a passive XY model, this results in topological caging, where orientational fluctuations that exhibit conventional diffusive behavior on a torus saturate on a Klein bottle to a finite value that we compute exactly in the thermodynamic limit. In models of active self-propelled particles with orientational degrees of freedom, topological caging persists despite continuously changing interaction neighborhoods. In an active Ising spin model, non-orientability enforces the coexistence of ordered anti-parallel domains with vanishing global polar order, a state that is absent on orientable domains.

cond-mat.stat-mech↗