K₂M^III₂(M^VIO₄)(PO₄)₂ (M^III = Fe, Sc; M^VI = Mo, W), Novel Members of the Lagbeinite-Related Family: Synthesis, Structure, and Magnetic Properties

Abstract

The possibility of PO(4)(3-) for MoO(4)(2-) partial substitution in the langbeinite framework has been studied by exploration of the K-Fe(Sc)-Mo(W)-P-O systems using the high-temperature solution method. It was shown that 1/3PO(4)(3-) for MoO(4)(2-) substitution leads to formation of three novel compounds K(2)Fe(MoO(4))(PO(4))(2), K(2)Sc(MoO(4))(PO(4))(2), and K(2)Sc(WO(4))(PO(4))(2) with slightly increased lattice parameters and significant distortion of the anion tetrahedra without structure changes. In contrast, the antiferromagnetic structure is modified by substitution in the low-temperature region. The structural peculiarities are discussed in light of bond-valence sums calculations.

Partial Substitution of Potassium with Sodium in the K2Ti2(PO4)3 Langbeinite‐Type Framework: Synthesis and Crystalline Structure of K1.75Na0.25Ti2(PO4)3

“…The BVS of P is close to 5. A slightly higher value of the total BVS for the formula unit depends on the obtained higher values of the BVS of Ti, which depends on the crystal structure and was reported in previous work …”

“…This approach was successfully applied for sites concurrently occupied by different elements in langbeinite‐type frameworks in previous investigations . As both K 1.75 Na 0.25 Ti 2 (PO 4 ) 3 and K 2 Ti 2 (PO 4 ) 3 should contain equal quantities of Ti III and Ti IV due to their electroneutrality, three variants of BVS calculations for the positions of Ti1 and Ti2 were performed.…”

“…As lightly higher value of the total BVS for the formula unit dependso nt he obtained higher values of the BVS of Ti,w hich depends on the crystal structure and was reported in previouswork. [31] Notably,o nly one of the crystallographic potassium sites in the L-KNTP structure is partially substituted by sodium. Preferable occupation of the K(1) position in L-KNTP by Na cations is substantiated by electronic structure calculations [a particular paper on thee lectronic structures of K 2Àx Na x Ti 2 (PO 4 ) 3 phosphates is in preparation]; however,i nt he Supporting Information we present some important results, namely,t he calculated partial densities of states for K 2 Ti 2 (PO 4 ) 3 and K 1.75 Na 0.25 Ti 2 (PO 4 ) 3 crystals[ see Figures S5 and S6;f or the optimized internuclear distances in K 1.75 Na 0.25 Ti 2 (PO 4 ) 3 ,s ee Table S2].…”

Rietveld refinement of the langbeinite-type phosphate K2Ni0.5Hf1.5(PO4)3

“…Langbeinite-related complex oxides have a variety of interesting properties, for example, ferroelectricity or ferroelasticity (Norberg, 2002). In particular, complex phosphates of this type have attracted attention for their high thermal and chemical stability, and many different combinations for structural substitutions are possible (Wulff et al, 1992;Slobodyanik et al, 2012). These characteristics made it possible to propose the family of langbeinite-type phosphates as successful hosts for the immobilization of radioactive waste (Orlova et al, 2011).…”

Interaction in the molten system Rb2O‐P2O5‐TiO2‐NiO. Crystal structure of the langbeinite‐related Rb2Ni0.5Ti1.5(PO4)3

“…The high‐temperature self‐flux crystallization is a typical experimental procedure for complex phosphates preparation. This method allows to grow the single crystals of known compounds as well as to obtain the new ones .…”