Time-of-flight neutron diffraction study of amorphous and liquid Ge-Te alloys

The short-range structure in amorphous and liquid GexTe1-x alloys with x less than or equal to 0.33 has been investigated through time-of-flight neutron diffraction measurements. The first sharp diffraction peak (FSDP) in the structure factor was observed in the amorphous state, implying that the structural units are partially connected each other, while, the FSDP was not obviously seen in the liquid state. The position and area (relating the coordination number) of the first peak in the amorphous distribution function were quite different from those in the liquid function. The difference function between distribution functions at x=0.16 and 0.20, indicated that the first coordination shell in the alloy is composed of two nearest neighbor correlations, i.e., Ge-Te and Te-Te. It was clarified from the first peak position of the difference function that both Ge-Te and Te-Te distances are 259 and 276 pm in the amorphous state, and 267 and 292 pm in the liquid state, respectively. After all, it can be concluded that Ge-Te alloys have a different local structure and different bonding nature among crystalline, amorphous and liquid states. These bonding differences result in a sharp change of electronic properties such as the magnetic susceptibility around crystallization and liquidus temperature.