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Average and local structure of apatite-type germanates and implications for oxide ion conductivity

DOI: 10.1021/acs.inorgchem.9b02544 DOI Help

Authors: Mathew S. Chambers (Durham University; Diamond Light Source) , Philip A. Chater (Diamond Light Source) , Ivana Radosavljevic Evans (Durham University) , John S. O. Evans (Durham University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Inorganic Chemistry

State: Published (Approved)
Published: October 2019
Diamond Proposal Number(s): 14188

Open Access Open Access

Abstract: Materials with the apatite structure have a range of important applications in which their function is influenced by details of their local structure. Here, we describe an average and local structural study to probe the origins of high-temperature oxide ion mobility in La10(GeO4)6O3 and La8Bi2(GeO4)6O3 oxygen-excess materials, using the low-conductivity interstitial oxide-free La8Sr2(GeO4)6O2 as a benchmark. For La10 and La8Bi2, we locate the interstitial oxygen, Oint, responsible for conductivity by Rietveld refinement and relate the P63/m to P1̅ phase transitions on cooling to oxygen ordering. Local structural studies using neutron total scattering reveal that well-ordered GeO5 square pyramidal groups form in the structure at low temperature, but that Oint becomes significantly more disordered in the high-conductivity, high-temperature structures, with a transition to more trigonal-bipyramid-like average geometry. We relate the higher conductivity of Bi materials to the presence of several Oint sites of similar energy in the structure, which correlates with its less-distorted low-temperature average structure.

Subject Areas: Chemistry, Materials

Instruments: I11-High Resolution Powder Diffraction

Added On: 21/10/2019 10:04


Discipline Tags:

Physical Chemistry Chemistry Materials Science Inorganic Chemistry

Technical Tags:

Diffraction X-ray Powder Diffraction