Spin singlet small bipolarons in Nb-doped BaTiO3

TL;DR

This study investigates how Nb doping in BaTiO3 leads to the formation of immobile spin singlet small bipolarons with significant binding energy, affecting electrical transport properties and revealing a crossover from band to hopping conduction.

Contribution

It provides experimental evidence of bipolaron formation and transport crossover in Nb-doped BaTiO3, a phenomenon rarely observed in polaronic systems.

Findings

Dopant electrons form immobile spin singlet small bipolarons with ~110 meV binding energy.

Electrical resistivity peaks at 15 K for x=0.2, indicating a transport crossover.

Observation of a transition from band to hopping conduction in the material.

Abstract

The magnetic susceptibility and electrical resistivity of n-type BaTi{1-x}Nb{x}O3 have been measured over a wide temperature range. It is found that, for 0 < x < 0.2, dopant electrons form immobile spin singlet small bipolarons with binding energy around 110 meV. For x = 0.2, a maximum in the electrical resistivity around 15 K indicates a crossover from band to hopping transport of the charge carriers, a phenomenon expected but rarely observed in real polaronic systems.