Temperature dependent X-ray studies of negative thermal expansion (NTE) ScF₃ thin films under strain

Bulk Scandium trifluoride (ScF₃) is known for a pronounced negative thermal expansion (NTE) over a wide range of temperature, from 10 K to 1100 K. The structure of ScF₃ can be described as an ABX₃ perovskite with an empty A-site. Growing films of ScF₃ allows for tuning the lattice constant, the thermal expansion, and the construction of devices based upon differential thermal expansion. We have investigated the growth of ScF₃ films on oxide and fluoride substrates using pulsed laser deposition (PLD). We have found growth routes for producing films with very good epitaxy and stability. Curiously, diffraction studies show narrow Bragg peaks along the principal crystallographic directions but substantial broadening for peaks along other directions, presumably associated with accommodating drastic differentials in thermal expansion. This report describes the temperature dependent X-ray studies of epitaxial NTE ScF₃ thin films grown epitaxially on a strongly positive thermal expansion (PTE) substrate.