From Online Dictionary of Crystallography
Orthohexagonal (Fr). Orthohexagonalen (Ge). Ortoesagonale (It). 直方六方 (Ja). Ortohexagonal (Sp).
The hexagonal lattice is frequently referred to an orthorhombic C-centred cell called orthohexagonal, whose volume is twice that of the conventional P cell. Three choices of the orthohexagonal cell are possible:
- C1, basis vectors change a, a+2b, c;
- C2, basis vectors change a+b, -a+b, c;
- C3, basis vectors change b, -2a-b, c.
The hexagonal symmetry is reflected in the metric specialisation of the orthohexagonal cell, which has b = a31/2. As a consequence, an orthorhombic crystal with conventional cell of type oC and b = a ratio close to 31/2 has a pseudo-hexagonal lattice.
- Chapter 1.5 of International Tables for Crystallography, Volume A, 6th edition