Intrinsic local symmetry-breaking in nominally cubic paraelectric BaTiO3
Whereas low-temperature ferroelectrics have a well-understood ordered spatial dipole arrangement, the fate of these dipoles in paraelectric phases remains poorly understood. Using density functional theory (DFT), we find that unlike the case in conventional non-polar ABO3 compounds illustrated here for cubic BaZrO3, the origin of the distribution of the B site off-centering in cubic paraelectric such as BaTiO3 is an intrinsic, energy stabilizing symmetry breaking. Minimizing the internal energy E of a constrained cubic phase already reveals the formation of a distribution of intrinsic local displacements that (i) mimic the symmetries of the low-temperature phases, while (ii) being the precursors of what finite temperature DFT Molecular Dynamics finds as thermal motifs. The implications of such symmetry breaking on the microscopic structures and anomalous properties in these kinds of PE materials are discussed.
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NSF-PAR ID:
10311424
Journal Name:
ArXivorg
ISSN:
2331-8422
Strong electronic interactions can drive a system into a state with a symmetry breaking. Lattice frustration or competing interactions tend to prevent symmetry breaking, leading to quantum disordered phases. In spin systems frustration can produce a spin liquid state. Frustration of a charge degree of freedom also can result in various exotic states, however, experimental data on these effects is scarce. In this work we demonstrate how in a Mott insulator on a weakly anisotropic triangular lattice a charge ordered state melts on cooling down to low temperatures. Raman scattering spectroscopy finds that$$\kappa$$$\kappa$-(BEDT-TTF)$${}_{2}$$${}_{2}$Hg(SCN)$${}_{2}$$${}_{2}$Cl enters an insulating “dipole solid” state at$$T=30\,{\mathrm{K}}$$$T=30\phantom{\rule{0ex}{0ex}}K$, but below$$T=15\,{\mathrm{K}}$$$T=15\phantom{\rule{0ex}{0ex}}K$the order melts, while preserving the insulating energy gap. Based on these observations, we suggest a phase diagram relevant to other quantum paraelectric materials.