iucr

commissions

principles
aperiodic crystals
biological macromolecules
crystal growth and characterization of materials
crystallographic computing
crystallographic nomenclature
crystallographic teaching
crystallography in art and cultural heritage
crystallography of materials
electron crystallography
high pressure
inorganic and mineral structures
international tables
journals
magnetic structures
mathematical and theoretical crystallography
neutron scattering
nmr crystallography
powder diffraction
quantum crystallography
small-angle scattering
structural chemistry
synchrotron and xfel radiation
xafs

congress

2020 iucr xxv
2017 iucr xxiv
2014 iucr xxiii
2011 iucr xxii
2008 iucr xxi
2005 iucr xx
2002 iucr xix
1999 iucr xviii
1996 iucr xvii
1993 iucr xvi
1990 iucr xv
1987 iucr xiv
1984 iucr xiii
1981 iucr xii
1978 iucr xi
1975 iucr x
1972 iucr ix
1969 iucr viii
1966 iucr vii
1963 iucr vi
1960 iucr v
1957 iucr iv
1954 iucr iii
1951 iucr ii
1948 iucr i

people

nobel prize

all
agre
anfinsen
barkla
boyer
w.h.bragg
w.l.bragg
brockhouse
de broglie
charpak
crick
curl
davisson
debye
deisenhofer
geim
de gennes
hauptman
hodgkin
huber
karle
karplus
kendrew
klug
kobilka
kornberg
kroto
laue
lefkowitz
levitt
lipscomb
mackinnon
michel
novoselov
pauling
perutz
ramakrishnan
roentgen
shechtman
shull
skou
smalley
steitz
sumner
thomson
walker
warshel
watson
wilkins
yonath

resources

commissions

aperiodic crystals
biological macromolecules
quantum crystallography
crystal growth and characterization of materials
crystallographic computing
crystallographic nomenclature
crystallographic teaching
crystallography in art and cultural heritage
crystallography of materials
electron crystallography
high pressure
inorganic and mineral structures
international tables
journals
magnetic structures
mathematical and theoretical crystallography
neutron scattering
NMR crystallography
powder diffraction
small-angle scattering
structural chemistry
synchrotron radiation
xafs

outreach

openlabs

calendar
LAAAMP Bruker OpenLab Benin
Bruker OpenLab Ghana
Malvern Panalytical OpenLab Turkey 2
Bruker OpenLab Côte d'Ivoire
LAAMP OpenLab Costa Rica
IUCr-IUPAP-ICTP OpenLab Senegal
Bruker OpenLab Cameroon
Rigaku OpenLab Bolivia
Bruker OpenLab Albania
Bruker OpenLab Uruguay 2
Rigaku OpenLab Cambodia 2
Bruker OpenLab Vietnam 2
Bruker OpenLab Senegal
PANalytical OpenLab Mexico 2
CCDC OpenLab Kenya
Bruker OpenLab Tunisia
Bruker OpenLab Algeria
PANalytical OpenLab Turkey
Bruker OpenLab Vietnam
Agilent OpenLab Hong Kong
PANalytical OpenLab Mexico
Rigaku OpenLab Colombia
grenoble-darmstadt
Agilent OpenLab Turkey
Bruker OpenLab Indonesia
Bruker OpenLab Uruguay
Rigaku OpenLab Cambodia
PANalytical OpenLab Ghana
Bruker OpenLab Morocco
Agilent OpenLab Argentina
Bruker OpenLab Pakistan

Once a contradiction in terms, aperiodic crystals show instead that “long-range order” has never been defined. Whatever it means, decades of intense research have shown it to be more complex and surprising than anyone suspected [Senechal (2015). *Acta Cryst*. B**71**, 250-251; doi: 10.1107/S2052520615009907]

The human brain is very skilled at detecting patterns and recognising order in a structure, and ordered structures permeate cultural achievements of human civilisations, be it in the arts, architecture or music. The ability to detect and describe patterns is also at the basis of all scientific enquiry.

Crystals are paradigms of ordered structures. While order was once seen as synonymous with lattice periodic arrangements, the discoveries of incommensurate crystals and quasicrystals has led to a more general perception of crystalline order, encompassing both periodic and aperiodic crystals. The current definition of crystals rest on their essentially point-like diffraction.

Considering a number of recently investigated model systems, with particular emphasis on non-crystalline ordered structures, the limits of the current definition are explored in a paper [Grimm (2015). *Acta Cryst*. B**71**, 258-274; doi:10.1107/S2052520615008409].

The current definition of a crystal is based on the currently known catalogue of periodic and aperiodic crystals. Scientists currently do not know of any materials that have aperiodically ordered structures beyond incommensurate crystals and quasicrystals. The definition of a crystal also reflects the lack of understanding of what constitutes order in matter, and in this sense should be seen as a working definition that may well need to be revised in the future. In crystallography, order is linked to diffraction, which makes sense because diffraction is the method of choice to experimentally determine the structure of a solid. Grimm demonstrates that there are ordered structures which are not captured by the current definition, either because their pure point diffraction fails to be finitely generated, or because they do not have any non-trivial point component in their diffraction.

While we do not know whether such structures are realistic in nature, it should become possible to manufacture materials with purpose-design structure and properties. In this sense, these are structures that are relevant and should be considered to be within the realm of crystallography.

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