[Cod-bugs] Possible Mislabeled Entry

[Saulius Gražulis]

Hi, once more,

On 2017-11-24 19:07, cod-bugs-owner at lists.crystallography.net wrote:
> Entry 1528427 (Al2O3) looks a lot like AlN structures published 
> elsewhere.  I think it may be mislabeled/misidentified.

I've looked in the original paper to double-check, and found the COD
entries are exactly as reported in the paper. The 1528427 is an unusual
hexagonal (H) phase, obtained after high-temperature reduction of
corundum. The authors claim that "the revealed H phase cannot be
identified as one of the known phases Al2 O3 with a hexagonal
structure". But they might have failed to notice similarity with AlN –
which might your small discovery :).

Actually, I've now looked into the COD tables:

> saulius at varanas ~/ $ mysql -u cod_reader -h sql.crystallography.net cod -e 'select file, doi, year, formula, calcformula, sg, a, b, c from data where ( doi = "10.1134/s1063774508070031" or formula = "- Al N -" ) and sg like "P 63%m c%" order by year desc'
> +---------+---------------------------+------+------------+-------------+------------+-------+-------+-------+
> | file    | doi                       | year | formula    | calcformula | sg         | a     | b     | c     |
> +---------+---------------------------+------+------------+-------------+------------+-------+-------+-------+
> | 1528427 | 10.1134/s1063774508070031 | 2008 | - Al2 O3 - | - Al2 O3 -  | P 63/m m c | 3.112 | 3.112 | 4.988 |
> | 9011657 | 10.1103/PhysRevB.48.4335  | 1993 | - Al N -   | - Al2 N2 -  | P 63 m c   |  3.11 |  3.11 |  4.98 |
> | 1535440 | NULL                      | 1993 | - Al N -   | - Al N -    | P 63 m c   | 3.144 | 3.144 | 5.046 |
> | 9008860 | NULL                      | 1963 | - Al N -   | - Al2 N2 -  | P 63 m c   | 3.111 | 3.111 | 4.978 |
> | 1010514 | 10.1007/BF01328124        | 1924 | - Al N -   | - Al N -    | P 63 m c   | 3.113 | 3.113 | 4.981 |
> +---------+---------------------------+------+------------+-------------+------------+-------+-------+-------+
and indeed, the reported supposedly Al2O2 phase from Danko2008 has
identical cell constants with other AlN phases! Maybe the Russian
authors converted Al2O3 to AlN upon heating, and did not notice it?
Although, their reducing atmosphere did not contain nitrogen...

Sincerely,
Saulius

-- 
Dr. Saulius Gražulis
Vilnius University Institute of Biotechnology, Saulėtekio al. 7
LT-10257 Vilnius, Lietuva (Lithuania)
fax: (+370-5)-2234367 / phone (office): (+370-5)-2234353
mobile: (+370-684)-49802, (+370-614)-36366