Study of protons in acceptor-doped KTaO3 crystals by IR and EPR techniques

Fu, S.Q.; Lee, W.K.; Nowick, A. S.; Boatner, L. A.; Abraham, M. M.

doi:10.1016/0022-4596(89)90171-0

Cited by 26 publications

(6 citation statements)

References 18 publications

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“…In a previous paper [4], EPR results show that nearly all Cu+ is converted to Cu 2 + upon 1% 02 treatment, in support of this suggestion. Finally, there remains the question of the role of the oxygen vacancies that compensate the acceptors in the case of a dry, reducing environment.…”

Section: Resultssupporting

confidence: 63%

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Conductivity Mechanisms in Acceptor Doped KTaO₃ Crystals

Scherban

Nowick

1990

MRS Proc.

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The electrical conductivity of perovskite-structured KTaO 3 crystals acceptor doped with Co, Cu or Fe was investigated after treatments in oxidizing and reducing atmospheres under both wet and dry conditions. Isotope effect measurements (using HO vs. D0O) show that, after treatments in wet gases of low P(OC), all the crystals are primarily protonic conductors, through a process of proton hopping with an activation energy close to 0.84 eV.Electron hole conduction dominates at high P(O) in the case of Fe and Cu doping. For Co-doped crystals, the conductivity is independent of P(0 2 ) up to 1 atm., indicating that ionic conduction predominates.There is no evidence of oxygen vacancy migration, leading to the conclusion that the activation energy for that process Is relatively high.

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Section: Resultssupporting

confidence: 63%

“…It has been shown through quantitative EPR measurements [4] that, rather than forming free holes in the valence band, the oxidation acts to change the valence of the dopant. To be specific, if we denote the acceptor In reduced form as A... (i.e.…”

Section: Introductionmentioning

confidence: 99%

Conductivity Mechanisms in Acceptor Doped KTaO₃ Crystals

Scherban

Nowick

1990

MRS Proc.

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“…This has been attempted in the literature 2 using a value of 10 14 s Ϫ1 for H as determined from single crystal studies of KTaO 3 . 17 However, a precise evaluation of the preexponential factors requires the direct determination of H , D , and T values in these perovskites. Experiments to accomplish this using inelastic neutron scattering are planned for the future.…”

Section: Resultsmentioning

confidence: 99%

Tritium Conductivity and Isotope Effect in Proton‐Conducting Perovskites

Brosha¹,

Birdsell²,

Costello³

et al. 1999

J. Electrochem. Soc.

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High temperature protonic-conducting oxides based on the perovskite structure have been studied extensively since their discovery in 1981. 1 The hydrogen and deuterium isotope conductivities in these oxides have been evaluated 2,3 recently, and their potential application as hydrogen separation membranes has been discussed. 4 However, there are no reported studies on the tritium ion-conduction in these perovskites. In this paper, we report the hydrogen (H), deuterium (D), and tritium (T) conductivities of three protonic conducting perovskites, viz. SrZr 0.9 Yb 0.1 O 2.95 , BaCe 0.9 Yb 0.1 O 2.95 , and SrCe 0.95 Yb 0.05 O 2.975 . The conductivity of tritium ions through these perovskites not only gives fundamental information regarding the hydrogen transport in these perovskites, but also allows for the exciting possibility of tritium separation using these oxides as an electrochemical membrane.The proton-conducting compounds that were investigated in this study were selected for the following reasons. (1) The strontium zirconates are known to have the best chemical stability in CO 2 containing atmospheres (stable in 20 vol % CO 2 at 700ЊC). 5 (2) The barium cerates have one of the highest magnitudes of protonic conductivity. 6 (3) The strontium cerates, having a high protonic transference number, are the most extensively studied proton-conducting perovskites. [7][8][9] Although a H/D isotope effect has been shown in proton-conducting perovskites, the data in the literature is neither extensive nor consistent enough to clearly establish a model for protonic conduction in these perovskites. 2 The measured difference in activation energies for the H-and D-ion conduction has eliminated the possibility of proton hopping governed by a classical theory and has given support to a semiclassical approach. This approach takes into consideration the difference in zero point energies between the ground state of H and D, given by Eq. 1 10where E H and E D are the activation energies for the H-and D-ion conduction, respectively, and H and D are the OH and OD stretching frequencies. However the pre-exponential factors presented in the literature do not obey the predictions of the semiclassical theory given by Eq. 2, c eff -concentration of mobile protons, and v ϭ unit cell volume.In this paper, we present the H-, D-, and T-ion conductivities of SrZr 0.9 Yb 0.1 O 2.95 and BaCe 0.9 Yb 0.1 O 2.95 , and attempt to explain the various factors that need to be addressed in order to unambiguously determine the conduction mechanism in these perovskites. ExperimentalSingle-phase perovskite samples of SrZr 0.9 Yb 0.1 O 2.95 , BaCe 0.9 Yb 0.1 O 2.95 , and SrCe 0.95 Yb 0.05 O 2.975 were prepared using standard solid-state methods by heating appropriate stoichiometric mixtures of BaCO 3 , SrCO 3 , CeO 2 , ZrO 2 , and Yb 2 O 3 at 1773 K for 20 h with two intermediate ballmilling steps. The formation of a single-phase orthorhombic perovskite was confirmed by powder X-ray diffraction using a Siemens D 5000 diffractometer. Dense ceramic samples (...

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“…The former is common for many perovskites and has, for example, been observed for potassium tantalate perovskite crystals grown from the melt. 12 To account for these two possible modes of proton incorporation and the cation vacancies that likely accompany hydroxyl group formation, [13][14][15][16] the chemical formula of potassium tantalate hydrate may be written as K x Ta y O 3−z (OH) z и nH 2 O, where x + 5y + z ‫ס‬ 6 is required for overall charge neutrality. The presence of cation vacancies as charge compensation defects is experimentally supported by the work of Shi and coworkers, 6 who observed by FTIR and electron paramagnetic resonance that the concentration of Ba 2+ vacancies increased with increasing OH − concentration in BaTiO 3 .…”

Section: A Perovskite Powdersmentioning

confidence: 99%