SYNCHROTRON X-RAY-IMAGING OF THE ELECTRON-DENSITY IN RFEO3 (R = Y, HO) USING AN APD DETECTOR

Structure factors for small hydrothermally grown yttrium and holmium o rthoferrites, RFeO3 (R = Y, Ho), were measured with focused synchrotro n radiation at wavelengths of 0.70 and 0.84 Angstrom using both scinti llation and high-speed avalanche photodiode (APD) detectors. Resulting APD Delta rho images showed striking correlations between aspherical electron densities around Fe and rare-earth metals. Approximate high s ymmetry in the hp images indicates that cations deform the electron de nsity far more strongly than the O atoms. The Ho--Fe magnetic interact ions appear to affect the electron density distribution of the Fe atom s and the magnetic phase transitions. Space group Pnma, orthorhombic, YFeO3 (APD): M-r = 192.76, a = 5.5931 (3), b, = 7.6102 (4), c = 5.2806 (3) Angstrom, V= 224.77 (2) Angstrom(3), Z= 3, D-x = 5.695 Mg m(-3); mu(0.84) = 15.56 mm(-1), F(000) = 356, T=293 K, R = 0.045, wR = 0.073, S = 4.83 (9) for 1282 unique reflections; HoFeO3 (APD): M-r= 268.78, a = 5.5922 (3), b = 7.6157 (5), c = 5.2798 (3) Angstrom, V= 224.86 (2) Angstrom(3), Z= 4, D-x = 7.939 Mg m(-3), mu(0.84) = 61.98 mm(-1), F(0 00) = 356, T= 293 K, R = 0.036, wR = 0.037,,S = 3.07 (6) for 1284 uniq ue reflections.