First experimental evidence of alluaudite-like phosphates with high Li-content: the (Na1-xLix)MnFe2(PO4)3 series (x = 0 to 1) (original) (raw)

Original paper

Hatert, Frédéric; Keller, Paul; Lissner, Falk; Antenucci, Diano; Fransolet, André-Mathieu

Abstract

Abstract Members of the Na1-xLixMnFe2(PO4)3 series, with the alluaudite structure type, were synthesized by solid-state reaction in air. The crystal structure refinement of the NaMnFe2(PO4)3 end-member (space group C2/c, Z = 4, a = 12.018(2), b = 12.565(3), c = 6.415(1) Å, β = 114.33(3) °), a synthetic compound with a chemical composition corresponding to the idealized composition of the Buranga alluaudite, was carried out to R1 = 0.026. The following cationic distribution was observed: Na+ + □ in A(1)and A(2)' (□ denotes lattice vacancies), Mn2+ in M(1), Fe3+ + Fe2+ in M(2). The A(2)' site exhibits a distorted gable disphenoid morphology and is found at the (0, y, ¼) (y ≈ 0) position in channel 2 of the alluaudite structure. The crystal structure of Na0.5Li0.5MnFe2(PO4)3(space group C2/c, Z = 4, a = 11.988(2), b = 12.500(3), c = 6.392(1) Å, β = 114.67(3°), refined to R1 = 0.034, leads to the cationic distribution: Li+ + Na+ + □ in A(2)', Na+ + □in A(1) , Mn2+ in M(1), Fe3+ + Fe2+ in M(2). Thus, the substitution mechanism involved in the replacement of Na by Li in the Na1-xLixMnFe2(PO)4)3 alluaudite-like compounds corresponds to □ + Na → Li + □, with x ranging from 0.00 to 0.90

Keywords

Na1-xLixMnFe2(PO4)3 • alluaudite structure type • solid-state reaction synthesis • crystal structure refinement • lithium crystal chemistry