Wurtzite crystal properties

The electronic properties of the extended crystal structures and the free building blocks have been compared. As free building blocks the linkers were represented in their dicarboxylate forms and the connector was considered as a part of the ZnO (wurtzite) crystal saturated with H atoms. 

ZnO normally has the hexagonal (wurtzite) crystal structure with lattice parameters a = 3.25 A and c = 5.12A (space group P63mc). The Zn atoms are tetrahedraDy coordinated to four O atoms, where the Zn d-electrons hybridize with the oxygen p-electrons. Layers occupied by zinc atoms alternate with layers occupied by oxygen atoms [94]. Whilst a bond between the Zn and O atoms exhibits covalent characteristic in the c-direction, it is mostly ionic in the o-direchon [95] consequently, ZnO single crystals have highly anisotropic properties. 

Xu Y-N, Ching WY (1993) Electronic, optical, and structural properties of some wurtzite crystals. Phys Rev B 48 4335-4351... 

The luminescent properties can be influenced by the nature of the activators and coactivators, their concentrations, the composition of the flux, and the firing conditions. In addition, specific substitution of zinc or sulfur in the host lattice by cadmium or selenium is possible, which also influences the luminescent properties. Zinc sulfide is dimorphic and crystallizes below 1020 °C in the cubic zinc-blende structure and above that temperature in the hexagonal wurtzite lattice. When the zinc is replaced by cadmium, the transition temperature is lowered so that the hexagonal modification predominates. Substitution of sulfur by selenium, on the other hand, stabilizes the zinc-blende lattice. 

Similar to the carbon system, BN exists in a soft hexagonal (h-BN) modification, a hard cubic (c-BN) one, and many others which are not very well crystallized, or amorphous. The properties of h-BN and c-BN are summarized in Table 1 [2-17], and the crystal structures of c-BN, w-BN (wurtzitic-BN), and h-BN are illustrated in Fig. 1. 

The unique properties of the stable d5 Mn2+ ion is reflected by the fact that MnS and MnSe crystallize in three modifications, in the rocksalt, the cubic sphalerite and the hexagonal wurtzite structure. While in the NiAs structure of MnTe the cations occupy the octahedral holes of a hexagonal close-packing of anions they occupy half of the tetrahedral holes of this packing in the ZnO type modification of MnS and MnSe. The non-metallic character is evident already from the fact that the structure is undistorted (c/a = 1.61 for MnS and 1.63 for MnSe) and that the cations really are at the centres of one set of tetrahedral holes and not at the centre of the bipyramidal holes composed of two tetrahedra of the two different sets. 

Cardona, M., and G. Harbeke (1965). Optical properties and band structure of wurtzite-type crystals and rutile. Phys. Rev. 137, A1467-76. 

Studies of x-ray diffraction (5-7), optical properties (6, 8), thermal expansion (, 9), thermal analysis (10-14). enthalpy (1), and decrepitation of single crystals (6, 9, ) indicate the existence of a reversible transition near 2100 C. 0-BeO is tetragonal with a structure related to rutile (5), while a-BeO is hexagonal close-packed with a wurtzite-type structure (1, IT). ... 

Besides group IV, the compounds by the atoms in groups III-V are also semiconductors, such as BN, BP, Bas, AIN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, and InSb. Except for the nitrides, all of these compounds crystallize into the zincblende structure. The nitrides are stable in the wurtzite structure. Meanwhile, the mixrnre crystals made of binary III-V compounds also have semiconducting properties, such as (Ga,Al)As, Ga(As,P),(In,Ga)As, and (In,Ga)(As,P). 

It is important to note that all ferroelectric crystals possess piezoelectric and pyroelectric properties. It was also found that all pyroelectric materials are piezoelectric, but the opposite is not true. For example, quartz is piezoelectric but not pyroelectric. At the same time zinc oxide with its wurtzite... 

---