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Figure 1 Structure of -Zr(HPO4)2. Octahedra represent ZrO6 group and tetrahedra represent HPO4 groups |
Figure 2 Synchrotron powder diffraction patterns showing the thermal transformations of -Zr(HPO4)2. |
INVESTIGATION OF THE THERMAL TRANSFORMATIONS OF -Zr(HPO4)2 USING IN SITU TEMPERATURE-RESOLVED POWDER DIFFRACTION.
CRYSTAL STRUCTURE OF TWO NEW
INTERMEDIATE PHASES.
Anne Marie Krogh Andersen1 and Poul Norby2
1 Department of Chemistry,
University of Odense, DK-5230 Odense M, Denmark. e-mail: amka@dou.dk
2 Department of Chemistry, University of Arhus,
DK-8000 Arhus C, Denmark.
Keywords: in situ,
synchrotron powder diffraction, zirconium phosphates.
Recently we have published the structure of a new zirconium hydrogen phosphate, t-Zr(HPO4)2 (1).t-ZrP has a 3-dimensional framework structure where ZrO6 octahedra are linked together by HPO4 tetrahedra forming a framework with a 4-ring channel extending along the c-axis. The OH groups of the hydrogen phosphates are pointing into the channel and form a hydrogen-bonded spiral along the 41-axis. Each hydrogenphosphate group both donates and accepts one hydrogen bond. The structure is shown in Figure 1.
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Figure 1 Structure of -Zr(HPO4)2. Octahedra represent ZrO6 group and tetrahedra represent HPO4 groups |
Figure 2 Synchrotron powder diffraction patterns showing the thermal transformations of -Zr(HPO4)2. |
In situ temperature-resolved powder diffraction data were recorded at beamline X7B at the National Synchrotron Light Source, Brookhaven National Laboratory. The sample was contained in a quartz capillary and heated to 900oC with a heating rate of 10C/min. The detector used was a Translating Imaging Plate (TIP) camera (2) built especially for time- and temperature-dependent experiments at beamline X7B (NSLS, BNL). Figure 2 shows a 3D representation of a small angular range of the powder patterns as a function of temperature.
Two new intermediate phases were observed and the crystal
structure solved. At 225C a reversible transformation to an
orthorhombic phase is observed. The unit cell parameters for this
phase are: a = 7.698(1), b = 8.187(1), and c =
5.402(1) A. At 315oC an irreversible transformation
connected with the loss of one mole of water is observed. The
unit cell parameters of the second intermediate phase are: a =
6.617(1), b = 8.285(2), c = 5.320(1) A. Finally at
615oC cubic zirconium pyrophosphate starts to form.
The structures of the two new intermediate phases will be
presented.
This work was supported by US DOE (DE-AC02-76CH00016, Div. Chem. Sci., BES).
