Dr Mark Welch
- Focus: Characterising new minerals with potential applications in materials science
We are using a range of techniques to characterise new minerals and investigate their potential for use in materials science.
We are using X-ray diffraction techniques to characterise minerals, many of which are new to science and have direct applications in materials technology.
We study two kinds of new mineral species:
- compositional variants of known-structure topologies, usually rock-forming minerals
- completely new structure topologies, often rare non-rock-forming minerals
Advances in X-ray diffractometry are allowing us to obtain structural data for very small crystals (less than 0.05 millimetres) and other previously challenging materials.
The characterisation of new mineral species requires close collaboration with curators and use of the Museum's mineral collections and equipment.
The structures and/or compositions of some new mineral species have potential applications in materials science, including:
- nano- or microporous sieves or ion exchangers
- fast-ion conductors
- piezo-electric devices
Read more about two recent examples of technologically relevant new minerals below.
Diegogattaite is a new mineral species with potential applications in ion- and gas-exchange and catalysis.
It is a nanoporous copper sheet silicate, closely related to the synthetic nanoporous copper silicates currently used in these processes.
Chemical formula: Na2CaCu2Si8O20·H2O
As natural examples of frustrated antiferromagnets (Kagome magnets), minerals of the paratacamite group have major applications in quantum data storage and battery technology.
We are studying:
- herbertsmithite and kapellasite (paratacamite-group minerals): Cu3Zn(OH)6Cl2
- haydeeite: Cu3Mg(OH)6Cl2
These minerals are natural examples of perfect spin-½ frustrated antiferromagnets in which an antiferromagnetic state is prevented by an ordered arrangement of non-magnetic elements (zinc and magnesium) within the polyhedral structure.
Such structures, known as Kagome phases, are significant for understanding 'quantum spin glasses'.
This new magnetically frustrated state has many potential applications, including:
- high-temperature superconductors
- data storage
- 'quantum-entangled' batteries as a new power source greatly superior to lithium-based batteries
We have discovered a novel reversible temperature-dependent transition (Tc ~ 380 K) between the paratacamite (2a R-3 trigonal superstructure) and herbertsmithite (1a R-3m substructure) that involves the operation of a rare dynamic J 04C0 ahn-Teller distortion of the mixed copper-zinc interlayer sites.
We are evaluating the significance of this transitional behaviour for herbertsmithite and kapellasite by examining recently discovered paratacamite species in which the substituent divalent cation varies (eg nickel, cobalt, magnesium).