Crystals of LiMn
2O
4undergo a first order structural phase transition near the room temperature. The high temperature (HT) form adopts a normal spinel-type structure (cubic,
Fd3m) with the octahedral sites populated statistically with heterovalent Mn
IIIand Mn
IVin the equal ratio. The low temperature (LT) form adopts a 3×3×1 superstructure (orthorhombic,
Fddd) with respect to the HT form, containing Mn1
III, Mn3
III, Mn4
IV, Mn5
IVand intervalent Mn2 atoms. The synchrotron X-ray single-crystal electron-density analysis revealed a bond-length fluctuation along the pseudo-tetragonal Jahn-Teller distortion parallel to the a axis in the heterocubane Mn2
4O9
4cluster which presumably shares three electrons among four
e-parentage orbitals of Mn2 and behaves as a core of Zener polaron. The heterocubane Mn2
4O9
4clusters are isolated with each other and embedded in an ordered way in the charge-ordered matrix containing Mn1
III, Mn3
III, Mn4
IVand Mn5
IV. The transition between the LT and HT forms of LiMn
2O
4can thus be regarded as an order-disorder transition of the Zener polarons. The molecular dynamics (MD) studies revealed that a periodical random switching of Mn valences, reflecting the e-parentage electron hopping model, greatly facilitates the Li-ion self-diffusion. Two distinct but coexistent processes have been proposed for the diffusion of Li atoms in the HT form of LiMn
2O
4.
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