The use of sol-gel, precursor dehydration and ion exchange methods to prepare low and negative thermal expansion oxides that would otherwise be difficult or impossible to access will be illustrated with work on CeP₂O₇, various M(III)M'(V)P₄O₁₄ compositions, GaZr₂P₃O₁₂ and related compounds. The chemical and physical properties of these materials, including the oxidation of GaZr₂P₃O₁₂ without destruction of its NZP framework, will be discussed.