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 orthoferrites, RFeO₃ (R = Y, Ho), were measured with focused synchrotron radiation at wavelengths of 0.70 and 0.84 Å using both scintillation and high-speed avalanche photodiode (APD) detectors. Resulting APD Δρ images showed striking correlations between aspherical electron densities around Fe and rare-earth metals. Approximate high symmetry in the Δρ images indicates that cations deform the electron density far more strongly than the O atoms. The Ho—Fe magnetic interactions appear to affect the electron density distribution of the Fe atoms 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) Å, V = 224.77 (2) ų, Z = 4, D_x = 5.695 Mg m⁻³, μ_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) Å, V = 224.86 (2) ų, Z = 4, D_x = 7.939 Mg m⁻³, μ_0.84 = 61.98 mm⁻¹, F(000) = 356, T = 293 K, R = 0.036, wR = 0.037, S = 3.07 (6) for 1284 unique reflections.