结晶矿物学 02-晶体生长

准晶体是其内部质点排列具有远程规律，但没有平移周期（赵 珊茸，2003），或不体现周期重复（潘兆橹，1993），即不 具格子构造。这种物态是介于晶体与非晶体之间的一种状态， 人们称之为准晶态或准晶体（quasicrystal）。
中国大百科全书，1993： 准晶体：原子等呈定向长程有序排列，但不作周期性平移重复， 具有与空间格子不相容的对称（如五次对称轴）的固体。
准晶体是一种固体，但其内部即不像非晶质体那样完全无序的 分布，又不像晶体那样的三维周期性平移有序。准晶体是其内 部结构呈自相似的配位多面体在三维空间作长程取向有序分布 的固体 （罗谷风，2010）。
准晶体 Quasicrystal：
Encyclopæ dia Britannica
quasicrystal, also called quasi-periodic crystal, matter formed atomically in a manner somewhere between the amorphous solids of glasses (special forms of metals and other minerals, as well as common glass) and the precise pattern of crystals. Like crystals, quasicrystals contain an ordered structure, but the patterns are subtle and do not recur at precisely regular intervalsodic crystal, or, in short, quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry（平移对称）. While crystals, according to the classical crystallographic restriction theorem, can possess only two, three, four, and six-fold rotational symmetries, the Bragg diffraction pattern of quasicrystals shows sharp peaks with other symmetry orders, for instance five-fold.
3.固相→结晶固相 ① 非晶固相→结晶固相 ② 结晶固相→结晶固相 同质多象转变 重结晶作用 固溶体分解 变质结晶
第二章 晶体生长理论
2-1 晶体的形成方式
1.液相→结晶固相
a) 熔体中结晶 b) 溶液中结晶 c) 蒸发结晶 d) 化学反应结晶
条件： a）降低温度-熔体过冷却 b）分散质达到过饱和 c）分散剂减少 d）化学反应生成不溶物质。
第二章 晶体生长理论
2-1 晶体的形成方式
2.气相—固相 条件：足够低的蒸气压
Quasicrystal Zn-Mg-Ho Diffraction
结晶学与矿物学
第二章 晶体生长理论
2-1 晶体的形成方式 2-2 晶核的形成 2-3 晶体生长模型 2-4 晶面的发育 2-5 影响晶体生长的外部因素 2-6 面角守恒定律
第二章 晶体生长理论
2-1 晶体的形成方式
晶体生长过程可以是： 1.液相→结晶固相 2.气相→结晶固相 3.固相→结晶固相
准晶体 Quasicrystal：
McGraw-Hill Science & Technology Encyclopedia：
Quasicrystal：A solid with conventional crystalline
properties but exhibiting a point-group symmetry inconsistent with translational periodicity. Like crystals, quasicrystals display discrete diffraction patterns, crystallize into polyhedral forms, and have long-range orientational order, all of which indicate that their structure is not random. But the unusual symmetry and the finding that the discrete diffraction pattern does not fall on a reciprocal periodic lattice suggest a solid that is quasiperiodic. Their discovery in 1982 contradicted a long-held belief that all crystals would be periodic arrangements of atoms or molecules.
Discrete diffraction pattern
(a) [110] diffraction pattern from LaCO3 crystal recorded by the SC200D CCD at camera length of 600mm, 200kV, full CCD 2x binning and 10sec exposure; (b) reversed contrast of left image.