Short-Range Structure of Proton-Conducting Perovskite BaIn_xZr_1-xO_3-x/2 (x = 0−0.75)

Abstract

In a systematic study we investigate the effect of dopant level and hydration on the short-range structure of the proton conducting perovskite-type oxide BaInxZr1−xO 3−x/2 (x = 0 − 0.75), using infrared and Raman spectroscopy. The results show that doping leads to significant local distortions of the average cubic structure of these materials. By increasing the In concentration from x = 0 to x = 0.75 new bands appear and grow in intensity in both the IR and Raman spectra, showing that the local distortions become successively more and more pronounced. The structural distortions are largely uncorrelated to the presence of oxygen vacancies, but instead are mainly driven by the size difference between the In 3+ and Zr 4+ ions, which leads to displacements of the cations and to tilting of the (In/Zr)O6 octahedra. Based on our results, we suggest that there is a threshold between x = 0.10 and x = 0.25 where the local structural distortions propagate throughout the whole perovskite structure. Comparison of our spectroscopic data with the proton conductivity reported for the same materials indicates that the presence of extended structural distortions are favorable for fast proton transport.

Short-range structure of proton-conducting BaM0.10Zr0.90O2.95 (M=Y, In, Sc and Ga) investigated with vibrational spectroscopy

“…Hydrated samples were prepared by annealing the powder samples at 275-300°C under a flow of Ar saturated with water vapor for 10 days. Further details of the sample preparation procedure can be found elsewhere [3].…”

“…In a previous work we investigated the short-range structure of the proton-conducting BaIn x Zr 1 − x O 3 − x/2 (x = 0, 0.10, 0.25, 0.375, 0.50, 0.625 and 0.75) perovskite series, using infrared (IR) and Raman spectroscopy [3].That study showed that the doping with In onto the B site of the perovskite leads to significant local distortions of the average cubic structure, that the distortions become more pronounced with increasing In concentration, and that they are largely uncorrelated to the presence of oxygen vacancies [3].…”

“…[3] to include also other types of dopant atoms. More specifically, we focus on the four cubic-structured proton-conducting perovskites BaM 0.10 Zr 0.90 O 2.95 (M = Y, In, Sc and Ga).…”

Preparation and characterization of Ce- and La-doped Ba2In2O5 as candidates for intermediate temperature (100–500°C) solid proton conductors

“…In order to keep the charge balance, oxygen leaves the structure, forming vacancies. Special cases of the acceptor-doped perovskites are the brownmillerite-structured oxides, such as Ba 2 In 2 O 5 , where B 4+ ions are completely substituted by lower-valent metal ions, M 3+ [10,11,15]. At lower temperatures (e.g., up to 925 • C for Ba 2 In 2 O 5 ) the oxygen vacancies are ordered in parallel tetrahedral oxygen vacancy layers, alternating with octahedral perovskite layers [16].…”

Proton Conductivity and Stability of Ba[sub 2]In[sub 2]O[sub 5] in Hydrogen Containing Atmospheres

“…[1][2][3] In these materials, the ideal perovskite A 2+ B 4+ O 3 2− is doped with lower-valent M 3+ ions, forming oxygen vacancies to compensate for the charge difference. 4 Existence of the oxygen vacancies favors oxygen ion transport and causes oxygen ion conduction in these materials. Moreover, mixed oxygen-ion and proton conduction has been found in these systems, with oxygen ion conduction predominant at high temperatures ͑typi-cally above 500°C͒ and protonic conduction predominant at low temperatures ͑typically below 500°C͒.…”