TY  - JOUR
AU  - Rodenbücher, Christian
AU  - Bihlmayer, Gustav
AU  - Korte, Carsten
AU  - Rytz, Daniel
AU  - Szade, Jacek
AU  - Szot, Kristof
TI  - An Operando Study of the Thermal Reduction of BaTiO3 Crystals: The Nature of the Insulator–Metal Transition of the Surface Layer
JO  - Crystals
VL  - 13
IS  - 8
SN  - 2073-4352
CY  - Basel
PB  - MDPI
M1  - FZJ-2023-03389
SP  - 1278 -
PY  - 2023
AB  - The insulator-to-metal transition upon the thermal reduction of perovskites is a well-known yet not completely understood phenomenon. By combining different surface-sensitive analysis techniques, we analyze the electronic transport properties, electronic structure, and chemical composition during the annealing and cooling of high-quality BaTiO3 single crystals under ultra-high-vacuum conditions. Our results reveal that dislocations in the surface layer of the crystal play a decisive role as they serve as easy reduction sites. In this way, conducting filaments evolve and allow for turning a macroscopic crystal into a state of metallic conductivity upon reduction, although only an extremely small amount of oxygen is released. After annealing at high temperatures, a valence change of the Ti ions in the surface layer occurs, which becomes pronounced upon the quenching of the crystal. This shows that the reduction-induced insulator-to-metal transition is a highly dynamic non-equilibrium process in which resegregation effects in the surface layer take place. Upon cooling to the ferroelectric phase, the metallicity can be preserved, creating a “ferroelectric metal.” Through a nanoscale analysis of the local conductivity and piezoelectricity, we submit that this phenomenon is not a bulk effect but originates from the simultaneous existence of dislocation-based metallic filaments and piezoelectrically active areas, which are spatially separated.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:001055257000001
DO  - DOI:10.3390/cryst13081278
UR  - https://juser.fz-juelich.de/record/1014684
ER  -