Distinctive features of the relationship between the structure and conductive properties of polycrystal Na3Fe2(PO4)3, obtained by the melt-quenching method of nanoarchitectronics

In this work, the features of the structure-conductivity relationship in polar (α) and ion-conducting (β and γ) phases of Na3Fe2(PO4)3 polycrystals obtained by the melt-quenching method have been investigated. Na3Fe2(PO4)3 polycrystals are synthesized by isothermal firing of glassy precursors (after grinding and pressing). The glassy precursors were prepared by melting a pre-calcined (350 C) mixture of initial reagents under the influence of thermal and infrared radiation energy and rapid cooling of the melt (or quenching). It was found that the deformations of the structure of polycrystals α-Na3Fe2(PO4)3 during synthesis by melt-quenching lead to an increase in the conductivity in polar (α) and ion-conducting (β and γ) phases because they contribute to the reduction of structural distortions of the samples. Polycrystals Na3Fe2(PO4)3 obtained by the melt-hardening method have high-quality crystallites, high density, and conductivity, and their synthesis is faster than samples obtained by other methods. The established advantages of synthesized polycrystals of α-Na3Fe2(PO4)3 are probably connected with deformations of structure and chemical activity of glassy precursors caused by nonequilibrium thermodynamic conditions of synthesis. For the first time, it was possible to detect domain structures in polycrystals of α-Na3Fe2(PO4)3 obtained by the melt-quenching method, which confirms the polarity of the α-phase, the appearance of which is associated with the ordered displacement of the cationic sublattice relative to the anionic sublattice under the influence of monoclinic distortion of the crystal framework.