Understanding the Crystallographic Phase Relations in Alkali-Trihalogeno-Germanates in Terms of Ferroelectric or Antiferroelectric Arrangements of the Tetrahedral GeX₃ Units

Journal Article · 17 December 2019 · Advanced Electronic Materials

DOI: https://doi.org/10.1002/aelm.201900887 · OSTI ID:1591755

Radha, Santosh Kumar ^[1]; Lambrecht, Walter R. L. ^[2]

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1. Case Western Reserve Univ., Cleveland, OH (United States); Case Western Reserve University
2. Case Western Reserve Univ., Cleveland, OH (United States)

The alkali-trihalogeno-germanates AGeX₃ with A: Rb or Cs and X a halogen (I, Br, Cl) along with the corresponding stannates (ASnX₃) and plumbates (APbX₃) reflect a large variety of crystal structures, some of which are of the perovskite type. These materials, better known as “halide perovskites” have recently gained worldwide attention as promising photovoltaic and more broadly opto-electronic materials. Yet, their stability problems relative to the non-perovskite phases are a major issue. It is shown that some of the phase relations in these materials can be understood in terms of the relative orientation of the GeX₃ tetrahedral units, which is ferroelectric (FE) in the perovskite phase but antiferroelectric (AFE) in the competing monoclinic phase. Electrostatic dipole interactions favor the AFE phase and the additional bond formation favors the FE phase. The change in phase is accompanied by a large change in band gap.

• Research Organization: Case Western Reserve Univ., Cleveland, OH (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: SC0008933
• OSTI ID: 1591755
• Journal Information: Advanced Electronic Materials, Journal Name: Advanced Electronic Materials Journal Issue: 2 Vol. 6; ISSN 2199-160X
• Publisher: WileyCopyright Statement
• Country of Publication: United States
• Language: English