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) A, c = 5.3807(7) A at 1200 °C and a = 3.3579(6) A, c = 5.398(1) A at 1340 °C. The lattice constants of bcc β-Sc were found to vary between a = 3.752(2) A at 1350 °C and a = 3.7572(8) A 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.