X-ray Birefringence from a Model Anisotropic Crystal

Whereas the phenomenon of birefringence is well-established and widely applied in the case of linearly polarized visible light (for example, underpinning the use of the polarizing optical microscope), the study of birefringence using linearly polarized X-rays is an essentially unexplored field. To address this issue, we report a material that exhibits ideal birefringence behavior at X-ray energies near the Br K-edge. The designed material, the 1-bromoadamantane/thiourea inclusion compound, gives experimental behavior in excellent agreement with theoretical predictions for the dependence of transmitted X-ray intensity on both X-ray energy and crystal orientation. Our results vindicate the potential to exploit X-ray birefringence to establish a detailed understanding of molecular polarization, particularly as an experimental strategy to determine the orientational distributions of specific bonds in solids, for example, in the case of partially ordered materials or materials that undergo order-disorder phase transitions.