Page 222 - PowerPoint Presentation

K R I S T A L I

Autori: Darja Nikolid, učenica VIII4 razreda, OŠ “Vuk Karadžid”, Isidora Todosid

Mentor: Ljiljana Grkovid, predmetni nastavnik, OŠ “Vuk Karadžid”, Beograd

REZIME

Kristali (najverovatnije od grčke reči koja znači "led") su minerali pravilnog
geometrijskog oblika određeni ravnim površima. Stvaranje kristala je posledica pravilnog ređanja
čestica (molekula, atoma, jona) u kristalnoj rešetki, koja se pruţa u sve tri prostorne dimenzije.
Formiraju se kada podlegnu procesu očvršćavanja. Pod idealnim uslovima, rezultat moţe biti
poseban monokristal, gde su svi atomi smešteni u istu kristalnu strukturu. Mnogi kristali se
formiraju istovremeno za vreme očvršćavanja, pa nastaju polikristali. Kristali simetrično srastaju
u udvojene kristale. Prostori između ćelija kristala nazivaju se kristalna rešetka. Simetrija
kristala razotkriva se u njegovoj prostornoj dimenziji. U idealnim aranţmanima kristali
pokazuju značajne nedostatke, da bi upravo ovi nedostaci kristala presudno uticali na mnoge
elektične i mehaničke osobine prirodnih materijala.

Ključne reči: kristali – kristalna struktura – udvojeni kristali – kristalna rešetka – kristalna
simetrija – kristalni nedostaci.

ABSTRACT

A crystal (most likely from a Greek word which means "ice") is a solid in which the constituent
atoms, molecules or ions are packed in a regularly ordered, repeating pattern extending in all
three spatial dimensions. Generally, crystals form when they undergo a process of solidification.
Under ideal conditions, the result may be a single crystal, where all of the atoms in the solid fit
into the same crystal structure. However, generally, many crystals form simultaneously during
solidification, leading to a polycrystalline solid. For example, most metals encountered in
everyday life are polycrystals. Crystals are often symmetrically intergrown to form crystal twins.
The spacing between unit cells in various directions are called crystal lattice. The
symmetryproperties of the crystal are embodied in its space group. Real crystals feature
defectsor irregularities in the ideal arrangements and it is these defects that critically determine
many of the electrical and mechanical properties of real materials.

Key words: crystal – crystal structure - crystal twins - crystal lattice - crystal symmetry –
crystal defects.