Crystal Structure, Magnetic Properties, and Ionic Conductivity of a New Mixed-Anion Phosphate Na₄Ni₅(PO₄)₂(P₂O₇)₂

Abstract

Single crystals of the new sodium phosphate Na 4 Ni 5 (PO 4 ) 2 (P 2 O 7 ) 2 have been isolated and their structure has been determined by X-ray diffraction techniques. This compound crystallizes in the monoclinic space group P2 1 /c with a ) 12.544(2) Å, b ) 6.596(1) Å, c ) 10.572(2) Å, β ) 103.731(3)°, and Z ) 2. Its three-dimensional structure can be described as formed by (Ni 5 P 2 O 22 ) ∞ infinite blocks parallel to the bc plane being the interblock linkages via P-O-P bridges of the diphosphate groups. There are tunnels along the [100] direction, crossing the (Ni 5 P 2 O 22 ) ∞ blocks, which host the sodium cations. The framework is built up from PO 4 tetrahedra, P 2 O 7 groups, NiO 6 octahedra, and Ni 2 O 9 units formed by face-sharing between two NiO 6 , which is unusual in these kinds of compounds. Magnetic measurements reveal the presence of antiferromagnetic interactions in the Ni 2+ sublattice, at about 8 K. The ionic conductivity, due to the motion of sodium ions, was measured at different temperatures (300-700 °C) in the frequency range 1-10 5 Hz. The determined activation energy was 0.99 eV and the conductivity at 500 °C was 2.8 × 10 -6 S cm -1 .

Synthesis, crystal structure and infrared spectroscopy of a new non-centrosymmetric mixed-anion phosphate Na4Mg3(PO4)2(P2O7)

“…Inorganic phosphates may represent perhaps one of the most interesting types of new inorganic materials, in large part, due to the ability of the tetrahedral PO 4 3− group to bond with other structural units. The studies of the phosphates Na 4 M II 3 (PO 4 ) 2 (P 2 O 7 ) (M = Mn, Co, Ni) [11][12] and Na 4 Ni 5 (PO 4 ) 2 (P 2 O 7 ) 2 [13] showed a quite unusual disordered distribution of the P 2 O 7 groups in the mixed frameworks of this series of isostructural compounds. To our knowledge the composition Na 4 Mg 3 (PO 4 ) 2 (P 2 O 7 ) has not been reported.…”

A Review on the Synthesis and Applications of Mesostructured Transition Metal Phosphates

“…On one hand, NiO 6 and PO 4 differ in bond lengths and angles [93]; on the other hand, nickel and phosphorus species are more apt to precipitation [94]. Kandori et al [95] first synthesized a uniform spherical NiP nanopartical with high mesoporosity (Figure 5j) and a surface area of 130 m 2 /g by using a hydrothermal procedure in the presence of a surfactant SDS.…”

“…The hydrolysis and condensation processes are much faster for metal ions than organic-inorganic hybrid silicates, presenting a big challenge for the controlled assembly of mesoporous transition metal phosphates with certain aimed morphologies. In some cases, precipitation can easily occur when both metal and phosphorus precursors are added in a solution [12,93]. For these reasons, there has been very few reports concerning the control of specific morphologies in mesostructured transition metal phosphate materials.…”

Trivalent Cation Substitution Effect into Layered Double Hydroxides Co2Fey Al1−y(OH)6Cl·nH2O: Study of the Local Order

“…The elements K and Q correspond to the dielectric relaxation and electrode phenomena, respectively. K is of the order of a few nF, and capacitance of this magnitude (considering the modulus) is observed when the grain-boundary response is dominating the whole (40). The refinements of the impedance spectra are displayed in Table 3 for the data obtained at 201C.…”