TY - JOUR
T1 - Average and Local Structure of Apatite-Type Germanates and Implications for Oxide Ion Conductivity
AU - Chambers, Matthew S.
AU - Chater, Philip A.
AU - Evans, Ivana Radosavljevic
AU - Evans, John S.O.
N1 - Publisher Copyright:
© 2019 American Chemical Society.
PY - 2019/11/4
Y1 - 2019/11/4
N2 - 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 P1¯ 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.
AB - 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 P1¯ 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.
UR - http://www.scopus.com/inward/record.url?scp=85073819778&partnerID=8YFLogxK
U2 - 10.1021/acs.inorgchem.9b02544
DO - 10.1021/acs.inorgchem.9b02544
M3 - Article
C2 - 31617356
AN - SCOPUS:85073819778
SN - 0020-1669
VL - 58
SP - 14853
EP - 14862
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 21
ER -