Synthesis and characterisation of novel metal pyrophosphates

Baker, Annabelle R. (2014). Synthesis and characterisation of novel metal pyrophosphates. University of Birmingham. Ph.D.

Preview

Baker14PhD.pdf
PDF - Accepted Version
Download (14MB)

Abstract

This thesis describes the synthesis, properties and structural characterisation of Mg $^2$ $^+$ , Mn $^2$ $^+$ and Ti $^4$ $^+$ pyrophosphates and Li and V substituted analogues.
α and β polymorphs of MgH $_2$ P $_2$ O $_7$ , were isolated by a novel acid melt synthetic route. Both polymorphs crystallised in monoclinic space groups, with α-MgH $_2$ P $_2$ O $_7$ isostructural with NiH $_2$ P $_2$ O $_7$ and β-MgH $_2$ P $_2$ O $_7$ isostructural with CaH $_2$ P $_2$ O $_7$ . Rietveld refinements of NPD data gave excellent fits to both structural models. MgLi $_0$ $_.$ $_8$ H $_1$ $_.$ $_2$ P $_2$ O $_7$ was also isolated with Rietveld refinement suggesting two similar possible structural models.
MnH $_2$ P $_2$ O $_7$ , a structural polymorph of β-MgH $_2$ P $_2$ O $_7$ was also synthesised via a similar route. Magnetic analysis revealed MnH $_2$ P $_2$ O $_7$ to be paramagnetic, with a small antiferromagnetic component. Incorporation of Li was again achieved via the addition of lithium carbonate during synthesis. Rietveld refinement of NPD data suggests a similar structure to that of MnH $_2$ P $_2$ O $_7$ and a composition of MnLi $_0$ $_.$ $_5$ H $_1$ $_.$ $_5$ P $_2$ O $_7$ .
A metastable polymorph of TiP2O7 has been successfully synthesised at low temperature and adopts a structure similar to the ideal cubic structure. Incorporation of vanadium resulted in an expansion of the unit cell. Both phases undergo a phase transition above 275°C to the ideal cubic structure. Addition of vanadium results in an unusual uniform spherical morphology unseen in parent phase.