High-pressure X-ray powder diffraction has been performed on corundumtype aFe,O, (hematite) in the pressure range up to 65 GPa using synchrotron radiation and a diamond anvil cell. A structural phase transformation has been observed with a transition pressure of about 55 GPa. The high-pressure form of Fe,O, is orthorhombic. The lattice parameters at 60GPa are a = 4.59(3)& b = 4.97( 3)& c = 6.68( 5)& Z = 4. The crystal structure is most probably a GdFe0,-type perovskite with space group Pbnm. The volume per formula unit in the orthorhombic phase is 10% smaller than in aFe,O,. It is suggested that the volume change is due to a combination of a valence change and a high-spin/low-spin transition. The bulk modulus, E,, and its pressure derivative, E& evaluated at zero pressure for aFe,O, are E, = 230(5)GPa and EA = 3.5(6).

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This invited article takes the opportunity occasioned by the approach of the millennium to look both backward and forward at the ills and the achievements of social work as a profession, at the changing political context in which we work, and at the successes and failures brought about by attempts to put the question of the worth of what we do beyond ideology through empirical research—in particular, through controlled experiments.

A 290 μm slice of z-cut, flux-grown, KTiOPO4 was subjected to square-wave electric field modulation at 1 Hz and examined using synchrotron radiation and a differential energy-dispersive x-ray spectroscopy system. Asymmetric Laue reflections (h0h and h̄0h) revealed the development of normally forbidden reflections (h odd) whose intensities grew until a threshold field of about 70 V/mm was reached, above which they disappeared. This effect was reversible and is interpreted as due to field-induced K+ ion disorder followed by domain reversal above a critical field with subsequent ordering. Symmetric Bragg reflections (00l) showed a dramatic effect: after a period of modulation, also at about 70 V/mm, the intensities began to fall and, at the same time, the peak widths began to narrow. This behavior resembles the transition from an ideally imperfect to an ideally perfect crystal and suggests that the crystal has been annealed electrically.