In-Situ Time-of-Flight Neutron Diffraction Study of High-Temperature α-to-β Phase Transition in Elemental Scandium

Lattice parameters for both hcp α -Sc and bcc β -Sc were determined between 1200 °C and 1400 °C from time-of-flight (TOF) neutron diffraction data collected from an elemental Sc sample vacuum sealed inside a niobium crucible. On heating, the high-temperature β -Sc phase first appeared between 1340 °C and 1350 °C, close to the reported transition temperature of 1337 °C. The lattice constants of hcp α -Sc were found to vary between a = 3.3522(4) Å, c = 5.3807(7) Å at 1200 °C and a = 3.3579(6) Å, c = 5.398(1) Å at 1340 °C. The lattice constants of bcc β -Sc were found to vary between a = 3.752(2) Å at 1350 °C and a = 3.7572(8) Å at 1400 °C. The average thermal expansion coefficient for the bcc β -Sc phase was 1.61 × 10 −5 °C −1 over the temperature range 1360 °C to 1400 °C. The average thermal expansion coefficient along the a -axis of hcp α -Sc between 1200 °C and 1340 °C was 1.46 × 10 −5 °C −1 . The average thermal expansion coefficient along the c -axis of hcp α -Sc between 1200 °C and 1340 °C was 2.22 × 10 −5 °C −1 .