Synthesis, structure and ionic conductivity in scheelite type Li_0·5Ce_0·5−xLn_xMoO₄ (x = 0 and 0·25, Ln = Pr, Sm)

DIPANKAR SAHA^a, GIRIDHAR MADRAS^a,b, ANINDA J BHATTACHARYYA^a and TAYUR N GURU ROW^a*

^aSolid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, 560 012, India
^bDepartment of Chemical Engineering, Indian Institute of Science, Bangalore, 560 012, India
*Corresponding author. E-mail: ssctng@sscu.iisc.ernet.in

MS received 25 August 2010;  revised 5 December 2010;  accepted 6 December 2010  

Abstract. Scheelite type solid electrolytes, Li_0·5Ce_0·5−xLn_xMoO₄ (x = 0 and 0·25, Ln = Pr, Sm) have been synthesized using a solid state method. Their structure and ionic conductivity (σ) were obtained by single crystal X-ray diffraction and ac-impedance spectroscopy, respectively. X-ray diffraction studies reveal a space group of I4₁/a for Li_0·5Ce_0·5−xLn_xMoO₄ (x = 0 and 0·25, Ln = Pr, Sm) scheelite compounds. The unsubstituted Li_0·5Ce_0·5Ln_xMoO₄ showed lithium ion conductivity ~10⁻⁵–10⁻³Ω⁻¹cm⁻¹ in the temperature range of 300–700°C (σ = 2.5 × 10⁻³Ω⁻¹cm⁻¹ at 700°C). The substituted compounds show lower conductivity compared to the unsubstituted compound, with the magnitude of ionic conductivity being two (in the high temperature regime) to one order (in the low temperature regime) lower than the unsubstituted compound. Since these scheelite type structures show significant conductivity, the series of compounds could serve in high temperature lithium battery operations.

Graphical Abstract. Scheelite type solid electrolytes, Li_0.5Ce_0.5-xLn_xMoO₄ (x = 0 and 0.25, Ln = Pr, Sm) have been synthesized via ceramic method. Their structure was solved by single crystal X-ray diffraction and ionic conductivity was measured from ac-impedance spectroscopy. These Scheelite type compounds could serve in high temperature lithium battery operations due to significant conductivity in the desired temperature range.

Keywords. Scheelite; ionic conductivity; ac-impedance spectroscopy.