Ostwald's rule of stages and metastable transitions in the hydrogen-water system at high pressure.

Although the hydrogenous analogue of the D2-D2O system has been well explored in the regimes above 1 GPa, and below 0.2 GPa, there have been very few studies in the region between these pressures. The recent discovery in the range 0.5-0.7 GPa of a new phase, C0, that possesses a new clathrate structure with a new H2O network, along with the proposal of another structure stable at similar conditions, has prompted further studies of the hydrogen water system in this intermediate pressure region. Here, we report the results of neutron-diffraction experiments that observed transitions from metastable to stable structures in the D2-D2O system around 0.2-0.3 GPa between 130 K and 280 K. These metastable structures were observed in the stability region of the sII hydrogen hydrate clathrate and computational studies of their relative enthalpies suggest that transition sequence observed is in line with Ostwald's 'Rule of Stages'.

On the stability of the disordered molecular alloy phase of ammonia hemihydrate.

The disordered-molecular-alloy phase (DMA) of ammonia hydrates [J. S. Loveday and R. J. Nelmes, Phys. Rev. Lett. 83, 4329 (1999)] is unique in that it has substitutional disorder of ammonia and water over the molecular sites of a body centred cubic lattice. Whilst this structure has been observed in ammonia di- and mono-hydrate compositions, it has not been conclusively observed in the ammonia hemihydrate system. This work presents investigations of the structural behaviour of ammonia hemihydrate as a function of P and T. The indications of earlier studies [Ma et al. RSC Adv. 2, 4290 (2012)] that the DMA structure could be produced by compression of ammonia hemihydrate above 20 GPa at ambient temperature are confirmed. In addition, the DMA structure was found to form reversibly both from the melt, and on warming of ammonia hemihydrate phase-II, in the pressure range between 4 and 8 GPa. The route used to make the DMA structure from ammonia mono- and di-hydrates--compression at 170 K to 6 GPa followed by warming to ambient temperature--was found not to produce the DMA structure for ammonia hemihydrate. These results provide the first strong evidence that DMA is a thermodynamically stable form. A high-pressure phase diagram for ammonia hemihydrate is proposed which has importance for planetary modelling.

Multi-extreme conditions at the Second Target Station.

Three concepts for the application of multi-extreme conditions under in situ neutron scattering are described here. The first concept is a neutron diamond anvil cell made from a non-magnetic alloy. It is shrunk in size to fit existing magnets and future magnet designs and is designed for best pressure stability upon cooling. This will allow for maximum pressures above 10 GPa to be applied simultaneously with (steady-state) high magnetic field and (ultra-)low temperature. Additionally, an implementation of miniature coils for neutron diamond cells is presented for pulsed-field applications. The second concept presents a set-up for laser-heating a neutron diamond cell using a defocused CO2 laser. Cell, anvil, and gasket stability will be achieved through stroboscopic measurements and maximum temperatures of 1500 K are anticipated at pressures to the megabar. The third concept presents a hybrid levitator to enable measurements of solids and liquids at temperatures in excess of 4000 K. This will be accomplished by a combination of bulk induction and surface laser heating and hyperbaric conditions to reduce evaporation rates. The potential for deployment of these multi-extreme environments within this first instrument suite of the Second Target Station is described with a special focus on VERDI, PIONEER, CENTAUR, and CHESS. Furthermore, considerations for deployment on future instruments, such as the one proposed as TITAN, are discussed. Overall, the development of these multi-extremes at the Second Target Station, but also beyond, will be highly advantageous for future experimentation and will give access to parameter space previously not possible for neutron scattering.

A profile of residents of old people's homes.

This paper describes the characteristics of the 450 residents of all statutory residential homes for the elderly within five local government districts in Northern Ireland. The residents are described in terms of demographic detail, prevalence of dementia and prevalence of problem behaviour. Results are comparable with those of other studies. There are more females, fewer are married and more are over the age of 75 years than would be predicted from the general population. Roughly half scored within the dementia range, with 56% of those over 85 years being demented. More than 33% had some degree of incontinence, 9% were immobile and 10% were physically aggressive at least once a week. Five percent were wanderers and nearly all residents required help with bathing.