"Negative thermal expansion (NTE; volume decrease on heating) is an unusual phenomenon of inherent interest and with important technological applications - e.g. in countering the more usual positive thermal expansion of other materials. The recent discovery of extreme NTE in many cyanide-containing materials has opened a new window into this unusual behaviour, revealing how the increased local flexibility of molecular units can have profound effects on many physical properties at the macroscopic scale - not only producing NTE, but also giving rise to unusual bulk and shear moduli and anomalous pressure-dependent properties. One of the most important pressure dependencies recently linked to NTE is pressure-induced amorphisation (PIA). This process - in which the application of pressure transforms the initially-periodic crystal lattice into a glass-like network - creates many new chemical bonds, absorbing large quantities of energy. There is clear potential to exploit PIA in high-stress applications, or even in the containment of nuclear waste. But because the fields of both NTE and PIA are really quite new (and particularly for cyanides), there is much about the pressure-dependent behaviour of NTE phases yet to be learned before their technological applications can be developed fully. This proposal aims to achieve a thorough, systematic and application-driven study of pressure-dependent behaviour in highly-flexible NTE phases. This builds on the expertise in high-pressure work found at Montpellier together with Dr Goodwin's background in studying NTE materials and structural transitions (including PIA). The specific aims are: 1. Understand the link between NTE and pressure-induced transformations such as PIA. 2. Identify and develop new NTE materials with technologically-relevant properties. 3. Quantify the pressure effects of host/guest interactions in nanoporous NTE phases. 4. Study the interplay between NTE and piezoelectricity in quartz-like NTE phases."