In the following, by "crystal" is meant any solid having an essentially discrete diffraction diagram, and by "aperiodic crystal" is meant any crystal in which three dimensional lattice periodicity can be considered to be absent. As an extension, the latter term will also include those crystals in which three dimensional periodicity is too weak to describe significant correlations in the atomic configuration, but which can be properly described by crystallographic methods developed for actual aperiodic crystals.

• Can Z, the number of formula units per unit cell, be a fraction? A report of the IUCr Commission on Crystallographic Nomenclature
  Acta Cryst. (2025), A81, 405-408.
• Seitz symbols for crystallographic symmetry operations

Teaching Edition of International Tables for Crystallography: Crystallographic symmetry

Editor: M. I. Aroyo

This sixth edition of what was previously known as the Brief Teaching Edition of Volume A was published in April 2021 (ISBN 978-0-470-97422-3) and may be ordered from Wiley. Its main aim is to provide an introduction to the space-group data in Volumes A and A1.

A brief publication history of International Tables

The International Tables started in 1935 with the first series, comprising two volumes, under the title Internationale Tabellen zur Bestimmung von Kristallstrukturen. The second series consisted of four volumes and was published between 1952 and 1974 with the title International Tables for X-ray Crystallography.

This sixth edition of what was previously known as the Brief Teaching Edition of Volume A provides an introduction to the basic crystallographic data for space groups found in Volume A, for symmetry relations between space groups in Volume A1 and for subperiodic groups in Volume E of International Tables for Crystallography, to magnetic space groups and to the symmetry database that forms part of International Tables Online at https://it.iucr.org.

The terms of reference are:

Christopher T. Chantler, Bruce A. Bunker, Hitoshi Abe, Masao Kimura, Matthew Newville and Edmund Welter

Prof Hiroyuki Oyanagi

Senior researcher and great pioneer of XAFS, Prof. Dr. Hiroyuki Oyanagi passed away on 13th March 2019.