An experimental and theoretical investigation of phonons and lattice instabilities in metastable decompressed SrGeO3 perovskite

A. Grzechnik, Andrew Chizmeshya, George Wolf, P. F. McMillan

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

We report detailed Raman and IR spectroscopic measurements for the decompressed high-pressure perovskite phase of SrGeO3. The appearance of a first-order Raman spectrum and slight splittings in the infrared bands suggest that the symmetry of the recovered metastable perovskite phase is lowered from Pm3m. This interpretation is fully supported by first-principles LDA calculations using the LAPW method, which indicate a small tetragonal distortion. The static lattice energy is lowered by 3.3 meV (per formula unit) by allowing rotational relaxation of the GeO6 octahedra. The calculations permit a reliable assignment of the zone centre phonon modes of SrGeO3 perovskite. The calculated pressure dependence of the ferroic IR-active modes is in excellent agreement with our measured data and reveals an incipient soft-mode behaviour in the tension regime. Further calculations of the GeO6 unit as a function of octahedral volume reveal instabilities to local off-centre Ge4+ displacements as the octahedra are expanded. This provides a detailed understanding of the large dielectric constant (e(0) ∼ 100) for this non-transition-metal-containing decompressed perovskite phase.

Original languageEnglish (US)
Pages (from-to)221-233
Number of pages13
JournalJournal of Physics Condensed Matter
Volume10
Issue number1
DOIs
StatePublished - Jan 12 1998

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ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

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