Developments in Ceramic Materials Research

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José M. Rojo, José L. Mesa and Teófilo Rojo
metaphosphate wavelengths of 2.41 Å (D2B) at 2 K were used in order to obtain a better
resolution of the magnetic data at lower angles. D1B has a 400 element linear multidetector
covering an angular range of 80 °. High flux and medium resolution of D1B at 2.52 Å were
used to study the thermal evolution of Fe(PO3)3 in the temperature range 1.5 – 20 K to resolve
the magnetic contributions of the neutron patterns. The magnetic and nuclear structures were
refined simultaneously, taking as starting parameter of each pattern those resulting from the
refinement of the preceding one. A pseudo-Voigth function was chosen to generate the line
shape of the diffraction peaks.
4. RESULTS AND DISSCUSION
4.1. Nuclear Crystal Structure Description
The M(PO3)3 (M= Ti, V, Cr, Mo and Fe) metaphosphates are the most condensed
phosphate systems where the metal ions present the unusual +3 oxidation state [5-10]. For
these compounds, the crystal structure may be described as formed by isolated (MO6)
octahedra linked through (PO3)∞ chains of (PO4) tetrahedra (see Figure 1a). Each (MO6)
group is bridged to six neighbouring (MO6) octaedra by phosphate groups and each
octahedron shares it six apices with different (PO4) tetrahedra. These tetrahedra lie in adjacent
layers and lead to a three-dimensional network, in which the metallic cations occupy three
different crystallographic positions for every metallic center.
The crystal structure for the other chromium phase, namely the hexametaphosphate, is
formed by (CrO6) octahedra linked through (PO4) tetrahedra belonging to (P6O18) 6- cycles
(see Figure 1b). The (CrO6) coordination polyhedra are not vertex- or edge-shared, and are
isolated by (PO4) tetrahedra. Each (CrO6) octahedron interacts with four (P6O18) 6- cycles,
three phosphorous atoms lie in the plane defined by the Cr(III) ions and the other three are
place below and above of the metallic cations in a perpendicular plane, leading to a threedimensional
network [14].
a
Figure 1 (Continued).
b c