Unveiling unknown phases and crystallization pathways in water under fast compression at HED
Scientists have used a dynamic anvil cell (dDAC) and supercompressed water. They were looking for (new) crystal phases in the ice VI stability regime showing that ice VI formation may happen through multi-step and multiple pathways.
Water at high-density
Water is the most abundant and important liquid on Earth, and is vital for life and for human survival. While we use water daily and utilise it in many important processes, there is still much we do not know about its properties. Though it is a relatively simple compound made up of only two elements— oxygen and hydrogen—it displays some of the largest number of anomalies in its properties. Scientists using European XFEL’s high energy density (HED) instrument are keen to uncover some of water’s previously hidden behaviours, in particular, the mysteries of water’s ‘unknown phases’.
A ‘phase’ in science refers to a chemical’s physical state, the most common being solid, liquid or gas. The phase of a compound usually changes as it is heated or cooled, and we are all familiar with the most common of these transitions: boiling water in a kettle, or freezing ice cubes. There are, however, many phases that chemicals can transition to and from, many of which arise in extreme conditions such as high pressures and low temperatures. Some of these phases are well described and encountered in our daily lives, even if we do not notice, for example, plasmas or glasses. But others are more unusual and can only be observed in the laboratory.
How water behaves on earth and elsewhere
“In our experiments, we focus on studying how water becomes ice,” says Geun Woo Lee, KRISS, South Korea. “There are lots of questions about how such a simple material forms so many different ice crystals. We think there are still ices that we don’t know of, that haven’t been discovered yet, but that can exist somewhere.”
The researchers work with ‘high-density water’ and use a piece of equipment at the HED instrument known as a diamond anvil cell (DAC) that can put the water under tremendous pressures, up to the levels found existing deep inside planets. They then use the European XFEL’s intense X-ray flashes to investigate the way in which water transitions from phase to phase, as well as uncovering new and previously unseen phases.
“Changes of phase happen really quickly, so we need strong X-rays and equipment that can measure extremely quickly,” Lee continues. “The HED instrument is what enables us to detect such fast phase changes and short-lived, unknown states.” The research will allow scientists to develop a clearer picture for how water behaves on Earth and elsewhere in the universe.
“A snowflake, or ice crystal, forms over 5000 different shapes. If you sail through an icy sea, or fly into a cold atmosphere, we can make better predictions about what will happen if we understand different types of ice,” Lee concludes. “And on other planets like Mars where you have extreme environments, we may expect water to have even more unusual behaviours. This kind of studies can tell us about water on other planets.”