Indexes in R-3c space group

[Marco Sommariva]

Good evening, I have a question about Miller indexes (h k l) in the space group R-3c (n° 167): in the article Chem. Mater. 2003, 15, 2084-2093 the authors writes: <<The XRD patterns clearly show reflections such as (3 0 3) which is normally forbidden in the R-3c space group... the space group is unambiguously R-3 rather than R-3c..>>.   I can't understand why (3 0 3) is forbidden in R-3c, since the general reflection condition is:  -h+k+l=3n. But this rule is present also in the space group R-3 (n°148) ! And what does it means <<normally forbidden >> ? Does 'n' must be always different from zero? Thanks a lot for explanations, marco       Marco Sommariva Department of Materials Science University of Milano - Bicocca Via R. Cozzi 53 - 20125 MILAN, ITALY Phone +39.02.6448.5141 (5142) Fax     +39.02.6448.5400 e-mail: [EMAIL PROTECTED]