铁电性
作者：互联网
铁电材料是一类特殊的电介质材料，存在可随电场翻转的自发极化，微观上通常会形成铁电畴结构 (自发极化方向相同的区域)。铁电性的结构根源来自非中心对称的极性点群，其出现总是伴随着从一个中心对称的空间群向其非中心对称的极性子群转变的铁电相变，宏观性能上表现出极化强度或电位移与电场强度间的强烈非线性-电滞回线。(抄自知社学术圈微信公众号: 钨青铜铁电体：蛮腰问何故？ (sohu.com) )
32个点群中，有 Centrosymmetry (中心对称) 有11个: Ci, C2h, D2h, C4h, D4h, C3i, D3d, C6h, D6h ,Th, Oh
对应的具体空间群 (空间群 - ghzphy - 博客园 (cnblogs.com)) 为:
the triclinic space group 2,
the monoclinic 10-15,
the orthorhombic 47-74,
the tetragonal 83-88 and 123-142,
the trigonal 147, 148 and 162-167,
the hexagonal 175, 176 and 191-194,
the cubic 200-206 and 221-230.
Point groups lacking an inversion center (non-centrosymmetric) can be polar, chiral, both, or neither.
A polar point group is one whose symmetry operations leave more than one common point unmoved. A polar point group has no unique origin because each of those unmoved points can be chosen as one. One or more unique polar axes could be made through two such collinear unmoved points. Polar crystallographic point groups include 1, 2, 3, 4, 6, m, mm2, 3m, 4mm, and 6mm.
A chiral (often also called enantiomorphic) point group is one containing only proper (often called "pure") rotation symmetry. No inversion, reflection, roto-inversion or roto-reflection (i.e., improper rotation) symmetry exists in such point group. Chiral crystallographic point groups include 1, 2, 3, 4, 6, 222, 422, 622, 32, 23, and 432. Chiral molecules such as proteins crystallize in chiral point groups.
The remaining non-centrosymmetric crystallographic point groups -4, 4-2m, -6, 6m-2, 4-3m are neither polar nor chiral.
来源: Chem. Rev. 2012, 112, 1163.
Pyroelectricity (from the two Greek words pyr meaning fire, and electricity) is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields.[1] Pyroelectricity can be described as the ability of certain materials to generate a temporary voltage when they are heated or cooled.[2][3] The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current. The leakage can be due to electrons moving through the crystal, ions moving through the air, or current leaking through a voltmeter attached across the crystal.
When materials having a polar point group crystal structure are heated or cooled, they may temporarily generate a voltage called pyroelectricity.
标签：polar,group,铁电性,point,中心对称,crystal,groups 来源： https://www.cnblogs.com/ghzhan/p/16314627.html