准晶的晶体学特征

Crystallographic Features of Quasicrystals

１０年前，具有五次旋转对称而无平移周期序的准晶问世，在与晶体及晶体学有关的学科领域里引起强烈反响。１０年来的系统研究澄清了准晶晶体学中的一些问题，如（１）准晶还是五重孪晶？（２）为什么要有五次旋转对称？（３）为什么会有准周期性？（４）稳定的准晶存在吗？（５）准晶与近似晶体相有什么异同？

The sensational discovery of quasicrystals with fivefold rotational symmetry and noperiodic translation order ten years ago made a strong impact to all solid state sciences based on crys-tals and crystallography,comprising metallurgy,materials science,chemistry,physics,mineralo-gy,etc.After a decennium of intensive study,many important aspects of this new class of materi-als and a new kind of ordered state with the so-called“ forbidden”symmetry and quasiperiodicityhave been made clear. Time is perhaps ripen to review the main advances of quasicrystal researchmade in the past ten years.The topics discussed in the present review are:(1)quasicrystal or five-fold twins?(2) why fivefold symmetry?(3) why quasiperiodicity?(4) stable quasicrystals;(5)crystalline approximants。