Crystal structure of CeRhGe3 from neutron data

11 Crystal structure of CeRhGe3 from neutron data  

Zaharko, V.K. Pecharsky and K.A. Gschneidner, Jr., unpublished. Neutron diffraction data were collected using the High Resolution Position Sensitive Detector Powder Diffractometer for Thermal Neutrons at the Paul Scherrer Institute, Switzerland (http //sinq.web.psi.ch/sinq/instr/hrpt.html). The same alloy was used in the two experiments (x-ray data in section 6.10, and neutron data in this section). 

Coherent neutron seattering lengths (b) are 4.84, 5.88, and 8.185 fm for Ce, Rh and Ge, respectively. Since for these three elements the neutron scattering ability accidentally increases with the decreasing atomic number, Ge is determined from neutron data with better accuracy than Ce. On the contrary, the x-ray scattering factors are proportional to the atomic number, and therefore, Ce is determined from x-ray diffraction with a better precision than Ge. 

The next strongest peak (No. 3) also belongs to the 2(a) site with the coordinate z = 0.754. Its shortest interatomic distances are ds-cei = 3.30 and 3.36 A and 53 oe2 = 3.27 A. All three correspond to Ce rather than to Rh, even though Ce is a light scattering atom when compared to Rh. Thus, after placing 2Ce in 2(a) with z= 0.754, the Rp = 19.8 % and the subsequently calculated Fourier map is illustrated in Table 6.26. 

So far three atoms have been confirmed, and the fourth strongest peak points to an atom that also belongs to the 2(a) site with z = 0.580. The only atom, which is missing from our model, is Rh. When 2 Rh atoms are placed in this site, the interatomic distance 5Rh ce = 1-75 A, which is too short. The fourth peak is therefore, a false maximum and it should be discarded. After the next strongest peak (No. 5) is tested, all distances are normal. The Rp = 16.3 % and the subsequent Fourier map is listed in Table 6.27, which now displays a sharp drop in peak heights after peak No. 4. The cross-section of 

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