TY - JOUR

T1 - Proton and Oxygen-Ion Conductivity of the Pure and Lanthanide-Doped Hafnates with Pyrochlore Structure

AU - Shlyakhtina, A. V.

AU - Lyskov, N. V.

AU - Kolbanev, I. V.

AU - Baldin, E. D.

AU - Kasyanova, A. V.

AU - Medvedev, D. A.

N1 - This study was subsidized by the Ministry of Sciences and Higher Education of the Russian Federation in frames of the Semenov Federal Research Center for Chemical Physics State contract “Next-generation nanostructured systems with unique functional properties” (reg. no. 122040500071-0). The material conductivity study is performed in part in frames of the Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry contract (the State reg. no. АААА-А19-119061890019-5).

PY - 2023/6/1

Y1 - 2023/6/1

N2 - In this work, a high-density ceramics Ln2Hf2O7 (Ln = La, Nd, Sm, Eu, Gd) were synthesized by mechanical activation followed by high-temperature synthesis at 1600°C (3–10 h) and their transport properties were compared with those of Ln2.1Hf1.9O6.95 (Ln = La, Nd, Sm, Eu) doped solid solutions. The total conductivity of ceramics was studied using impedance spectroscopy and dc four-probe method; for Ln2Hf2O7 (Ln = Sm, Eu), by determining the total conductivity as a function of oxygen partial pressure. The maximum oxygen-ion conductivity was observed for Gd2Hf2O7 (~1 × 10–3 S/cm at 700°C); it was shown to approach the conductivity of Gd2Zr2O7 (~2 × 10–3 S/cm at 700°C) for the first time. Thus, the gadolinium hafnate can be a promising material for further doping in order to obtain highly conductive electrolytes. Among pure rare-earth hafnates, the proton conductivity was reliably observed for Nd2Hf2O7 only; however, ac measurements detected low-temperature proton conductivity in the Gd2Hf2O7 up to 450°С as well. With a decrease in the lanthanide ionic radius, the oxygen-ion conductivity increased in the Ln2Hf2O7 (Ln = La, Nd, Sm, Gd) series. Although the conductivity of samarium hafnate is an order of magnitude lower than that of Gd2Hf2O7, it has a wide range of oxygen-ion conductivity (~10–18–1 atm at 700, 800°C); there is no contribution from hole conductivity in air, in contrast to Eu2Hf2O7. Among doped Ln2.1Hf1.9O6.95 pyrochlore solid solutions (Ln = La, Nd, Sm, Eu), the proton conductivity of ~8 × 10−5 S/cm at 700°C was shown in Ln2.1Hf1.9O6.95 (Ln = La, Nd). With a decrease in the lanthanide ionic radius, the proton conductivity disappeared; the oxygen-ion one, increased.

AB - In this work, a high-density ceramics Ln2Hf2O7 (Ln = La, Nd, Sm, Eu, Gd) were synthesized by mechanical activation followed by high-temperature synthesis at 1600°C (3–10 h) and their transport properties were compared with those of Ln2.1Hf1.9O6.95 (Ln = La, Nd, Sm, Eu) doped solid solutions. The total conductivity of ceramics was studied using impedance spectroscopy and dc four-probe method; for Ln2Hf2O7 (Ln = Sm, Eu), by determining the total conductivity as a function of oxygen partial pressure. The maximum oxygen-ion conductivity was observed for Gd2Hf2O7 (~1 × 10–3 S/cm at 700°C); it was shown to approach the conductivity of Gd2Zr2O7 (~2 × 10–3 S/cm at 700°C) for the first time. Thus, the gadolinium hafnate can be a promising material for further doping in order to obtain highly conductive electrolytes. Among pure rare-earth hafnates, the proton conductivity was reliably observed for Nd2Hf2O7 only; however, ac measurements detected low-temperature proton conductivity in the Gd2Hf2O7 up to 450°С as well. With a decrease in the lanthanide ionic radius, the oxygen-ion conductivity increased in the Ln2Hf2O7 (Ln = La, Nd, Sm, Gd) series. Although the conductivity of samarium hafnate is an order of magnitude lower than that of Gd2Hf2O7, it has a wide range of oxygen-ion conductivity (~10–18–1 atm at 700, 800°C); there is no contribution from hole conductivity in air, in contrast to Eu2Hf2O7. Among doped Ln2.1Hf1.9O6.95 pyrochlore solid solutions (Ln = La, Nd, Sm, Eu), the proton conductivity of ~8 × 10−5 S/cm at 700°C was shown in Ln2.1Hf1.9O6.95 (Ln = La, Nd). With a decrease in the lanthanide ionic radius, the proton conductivity disappeared; the oxygen-ion one, increased.

UR - http://www.scopus.com/inward/record.url?partnerID=8YFLogxK&scp=85163782733

UR - https://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=tsmetrics&SrcApp=tsm_test&DestApp=WOS_CPL&DestLinkType=FullRecord&KeyUT=001021011000002

UR - https://elibrary.ru/item.asp?id=62027909

U2 - 10.1134/S1023193523060058

DO - 10.1134/S1023193523060058

M3 - Article

VL - 59

SP - 449

EP - 460

JO - Russian Journal of Electrochemistry

JF - Russian Journal of Electrochemistry

SN - 1023-1935

IS - 6

ER -