A crystal grows in a hot solution like a lollipop on a stick in sugar syrup. Only instead of sugar, it's germanium oxide, and instead of a stick, there's a tiny seed. By changing the solution composition, you can make the crystal grow faster, alter the shape of its faces, or even turn it into a mass of many small crystallites.
Scientists grew germanium oxide crystals from a mixture of molybdenum oxide and lithium carbonate. It turned out that changing the molybdenum fraction by just one and a half percent — from 40% to 41.5%—makes the crystal change its proportions: it becomes more elongated, although the facets remain sharp. And if you add even more molybdenum, growth proceeds in all directions at once, and instead of one large crystal, you get a polycrystalline mass.
Such precise control over shape and growth rate is important for industry. Germanium oxide is a semiconductor with a very wide bandgap, meaning it can operate at high voltages and in the ultraviolet range. It can be used to make power transistors and sensors that are not afraid of overheating. And the grown crystals serve as substrates — the foundation on which thin films for devices are built.
Now manufacturers can tailor the solution composition to a specific task: need a long crystal, use one proportion; need a flat one, use another. This speeds up and cheapens the path from a laboratory sample to a mass-produced device.
The rutile form of germanium oxide is named after the mineral rutile, which makes up titanium white, the most common white pigment in paints and plastics.