Two time-of-flight powder diffractometers have operated at the Intense Pulsed Neutron Source (IPNS) since August 1981. These instruments use dedicated microcomputers to focus time-of-flight events so that data from different detectors can be summed into a single histogram. Thus, large multidetector arrays can be employed at any scattering angle from 12 to 157°. This design permits data to be collected over a uniquely wide range of d spacings while maintaining high resolution and count rates. The performance of the two instruments is evaluated by analyzing data from a standard Al₂O₃ sample by the Rietveld method. These instruments provide the capability for moderate- to high-resolution measurements with the duration of a typical run being a few hours.

The lattice parameters, bond lengths and bond angles of Si₂N₂O have been determined at pressures up to 23 kbar by time-of-flight neutron diffraction. The average compressibility coefficients of the orthorhombic structure are K_a = 21 (2), K_b = 34 (2), K_c = 25 (2) and Kν = 79 (4) x 10⁻⁵ kbar⁻¹, though the anisotropy is more pronounced at lower pressures with Ka (at zero pressure) estimated to be 10 (8) × 10–5 kbar⁻¹. The major contribution to the compression is a cooperative rotation of adjacent SiN₃O tetrahedra brought about by a decrease in the Si–O–Si bond angle. The shortening of one Si–N bond within each tetrahedron further enhances the compression, especially along the b direction.