We rarely stop to think of the advances in materials that underlie our material advances. Yet almost all our personal gadgets and technological innovations have something in common: they rely on some extremely unfamiliar materials from the nether reaches of the periodic table. Even if you have never heard of the likes of hafnium, erbium or tantalum, chances are there is some not too far from where you are sitting.You could soon be hearing much more about them, too. Demand for many of these unsung elements is soaring, so much so that it could soon outstrip supply. That's partly down to our insatiable hunger for the latest gadgetry, but increasingly it is also being driven by the green-energy revolution. For every headphone or computer hard-drive that depends on the magnetic properties of neodymium or dysprosium, a wind turbine or motor for an electric car demands even more of the stuff. Similarly, the properties that make indium indispensable for every touchscreen make it a leading light in the next generation of solar cells.All that means we are heading for a crunch. In its Critical Materials Strategy, published in December last year, the US Department of Energy (DoE) assessed 14 elements of specific importance to clean-energy technologies. It identified six at "critical" risk of supply disruption within the next five years: indium, and five "rare earth" elements, europium, neodymium, terbium, yttrium and dysprosium. It rates a further three - cerium, lanthanum and tellurium - as "near-critical".