Single-phase magnesium-aluminium layered double hydroxide (LDH) intercalated with dihydrogen phosphate was successfully produced by hydration of nanopowder of the respective mixed metal oxide (MMO) obtained using sol-gel based method followed by a two-step anion exchange hydroxide-to-chloride and chloride-to-phosphate. The MMO with the metal cation ratio of Mg/Al = 2:1 was prepared using the aqueous sol-gel method. Processes of the parent Mg₂Al-OH LDH formation and the successive anion-exchanges, ОН⁻ → Cl⁻and Cl⁻ → H₂PO₄⁻, were considerably accelerated via the application of high-power (1.5 kW) ultrasound. The crystalline phases formed at all stages of the Mg₂Al-H₂PO₄LDH production were characterized using X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, inductive coupled plasma optical emission spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Based on the data of chemical analysis and the XRD data, the type of the intercalated phosphate anion was determined and the arrangement of this anion in the interlayer was modelled.

The present work investigates the crystallization and phase evolution of amorphous calcium phosphate (ACP) partially substituted with smaller (Mg²⁺, Zn²⁺) and larger (Sr²⁺, Ba²⁺) divalent ions in the range from 1 to 10 mol % (M/P = 1.5:1). It has been demonstrated that the crystallization of ACP to tricalcium phosphate (TCP) and subsequent phase transformations between TCP polymorphs strongly depend on the nature and concentration of the substituents in the ACP matrix. Two different effects induced by the presence of foreign ions were observed. Substitution with smaller ions did not affect the crystallization temperature but promoted the formation of β-TCP at a significantly lower temperature compared to the phase evolution of pristine ACP. Moreover, the effect of Mg was found to be more significant than that of Zn in the transformation of metastable α-TCP to β-TCP. On the other hand, substitution with larger ions retarded the crystallization process, which was observed at elevated temperatures. While the substitution level of 10 mol % of Sr did not affect the thermal stability of metastable α-TCP, the presence of 10 mol % of Ba stabilized α-TCP crystal structure and totally prevented the phase transition to β-TCP.