Solid-phase synthesis of MINi2MIV(PO4)3 compounds (МI – Li, Na, K; MIV – Ti, Zr, Sn)

Abstract

Double phosphates compounds may possess catalytic, magnetic, electrophysical, non-linear optical properties and are used as monocrystals or polycrystals, ceramics etc. The tailor-made synthesis of double phosphates of alkali and multivalent metals is the basis for the in-depth research and investigation of physical and chemical properties, composition and structure of the compounds to be used for the development of new materials for multi-purpose use.

Episodic syntheses of compounds M^I₃M^IІM^IV(PO₄)₃, M^I₂M^IIM^IV(P₂O₇)₂, M^I₂M^II(PO₃)₄ and М^ІM^ІІ₄(РО₄)₃₃ (where М^I – Li, Na, K; М^IІ – Mn, Co, Ni; M^IV – Zr), were made from various starting materials by the sintering method. After all, the selection of compounds for the synthesis of compounds of this type is a rather difficult task, often impossible. A systematic approach to the selection of starting reagents, temperature regime, interaction time between components are factors that can be adjusted and operated to achieve the target.

The work used the method of solid-phase synthesis, after working out the synthesis method on the “model” Na₂NiZr(P₂O₇)₂. The synthesis was carried out starting from Na₂CO₃, NiO, CoO, ZrO₂, ammonium hydro- and dihydrogen phosphate. The synthesis of compounds was carried out based on preliminary derivatographic studies of the passage of processes according to the corresponding reaction schemes. Completeness of synthesis stages was monitored at all stages using physico-chemical research methods.

The DTA method confirmed the possibility of solid-phase synthesis of complex phosphate compounds that contain several transition metals – M^INi₂M^IV(PO₄)₃ (where М^I – Li, Na, K; M^IV – Ti, Zr, Sn). The optimal temperature conditions for obtaining a number of phosphate compounds based on various starting substances for their synthesis have been found.

The synthesized compounds were investigated by X-ray diffraction, DTA and IR spectroscopy, and their complete chemical analysis was carried out. The influence of a number of factors on the conditions of production of phosphate compounds of the M^INi₂M^IV(PO₄)₃ (where М^I – Li, Na, K; M^IV – Ti, Zr, Sn) has been found. It can be assumed that the ionic conductivity in the synthesized compounds is of the “NASICON” type, and therefore the synthesized substances can be used as functional materials with valuable electro-physical properties.