Pyrochlores are structures which have formula A 2 B 2 O 7-δ , with A and B denoting two possible cation sites and δ the possible oxygen defect. Stoichiometric pyrochlores, where δ = 0 feature metal ions with one of two combinations of formal charge: A(II)B(V) or A(III)B(IV). ), which are predicted to crystallize in space group Imm2. N.B. the naming convention for pyrochlores is that the A site is the larger metal ion of lower charge and appears first in the formula, but to avoid confusion we will use the compound names given in the A-lab paper, which in each case place the B site ion first. It should be pointed out that for each of the five compounds listed above, there exists a reported, disordered version of the material on the ICSD. In fact all of the B sites in question were incorporated into lead antimony pyrochlores by Cascales and coworkers in a series of papers in 1985-86, and each is reported by them as consisting of random B site substitutions, retaining the pyrochlore symmetry F d 3m. Since the predicted structures for these five compounds are just B site ordered versions of the known disordered structures, we again emphasise that evidence of the ordering must be found in the characterisation in order to prove the formation of the ordered phase. We note that the x-ray scattering factors between M and Sb are very similar for M = In, Hf, Sn, meaning that any ordering of these elements in the synthesised materials would be very difficult to detect via XRD. Our own refinement is given in Fig. . We find it necessary to include impurity phases NiSb 2 O 6 (ICSD# 426852), and NiO (ICSD# 9866) to match all the Bragg peaks. We attempted the fit with Zn-Ni-Sb spinels with different Ni contents from the ICSD. We show the fit with Zn 6 NiSb 2 O 12 (ICSD# 109465), although other Ni contents gave very similar fits and we do not think we can differentiate between them. Therefore, in this case, the ordered B site spinel from the Materials Project is clearly not present, as the strong low angle ordering peak that is predicted to appear at 17.9°is absent from the experimental data. The spinel phase that is present matches well with known Zn-Ni-Sb spinels with disordered B site cations. We conclude in the absence of any further evidence, that this is not a new material. The compound Zn 2 Cr 3 FeO 8 is predicted by A-lab to have ordered Cr and Fe ions on the B site, but is otherwise identical to the normal spinel structure. A series of solid solutions between ZnCr 2 O 4 and ZnFe 2 O 4 , including the exact composition predicted, was reported in 1970, and the B site cations were described as disordered. Due to the small difference in scattering factor between Fe and Cr, there is only minimal difference in PXRD pattern between the predicted, ordered structure and the known, disordered structure. In addition, the reported PXRD pattern of Zn 2 Cr 3 FeO 8 also contains several unmodelled impurity peaks which likely correspond to binary oxides of the metals. In the absence of any other evidence, we conclude that Zn 2 Cr 3 FeO 8 is not a new material and is the disordered B site spinel described in 1970. Thus this falls under error number three.