Journal Article

FZJ-2023-03389

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png An Operando Study of the Thermal Reduction of BaTiO3 Crystals: The Nature of the Insulator–Metal Transition of the Surface Layer

Rodenbücher, C. (Corresponding author)FZJ* ; Bihlmayer, G.FZJ* ; Korte, C.FZJ* ; Rytz, D. ; Szade, J. ; Szot, K.

2023
MDPI Basel

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Please use a persistent id in citations: doi:10.3390/cryst13081278  doi:10.34734/FZJ-2023-03389

Abstract: 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.

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Contributing Institute(s):

1. Elektrochemische Verfahrenstechnik (IEK-14)
2. Quanten-Theorie der Materialien (PGI-1)

Research Program(s):

1. 5211 - Topological Matter (POF4-521) (POF4-521)
2. 1231 - Electrochemistry for Hydrogen (POF4-123) (POF4-123)

Appears in the scientific report 2023

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