Hollandite, structure

Figure 2. In this low-symmetry, metal-metal bonded adaptation of the well-known hollandite structure the chains forming the four sides of each tunnel are related in pairs by P 1 symmetry.

Figure 4.15 Hollandite structure. The shaded diamonds represent chains of edge-shared MnC>6 octahedra and the shaded circles Ba2+. The light and heavy shading represent octahedra and atoms at two different heights. The unit cell is outlined.

A hollandite structure phase containing Ba, Ti, Al, and O is fabricated with the aim of immobilizing radioactive nuclides, (a) What is the formula of the hollandite (b) It is desired to replace 10% of the Ba with radioactive K. What would the formula of the new phase be (c) It is desired to replace 35% of the Ba with radioactive Sr. What would the formula of the new phase be (d) It is desired to replace 17% of the Ba with radioactive La. What would the formula of the new phase be ... 

Akaganeite, P-FeOOH, is named after the Akagane mine in Japan where it was first discovered (Mackay, 1962). It occurs rarely in nature and is found mainly in Cl-rich environments such as hot brines and in rust in marine environments. Unlike the other FeOOH polymorphs, it has a structure based on body centered cubic packing of anions (bcp) (hollandite structure) and contains a low level of either chloride or fluoride ions. It has a brown to bright yellow colour. 

Post, J. E., Von Dreele, R. B. Buseck, P. R. 1982. Symmetry and cation displacements in hollandites structure refinements of hollandite, cryptomelane and priderite. Acta Crystallogra-phica, B38, 1056-1065. 

The astute reader will recognize that this compound is a metal-metal bonded adaptation of the well-known hollandite structure (19). Further, the metal cluster configuration is like that in CsNb Cl.. (20), though the latter compound possesses a double layer structure rather than the tunnel structure observed here. Finally these new structures provide only a glimpse of what is possible, and an excitement about new compounds of unusual structure and properties yet to come from studies of highly reduced ternary and quaternary refractory metal oxide systems. 

We noted earlier the change of a synthetic sanidine (KAlSisOs) under high pressure (120 kbar, 900°C) to the hollandite structure, in which Si is 6-coordi-nated. ... 

Figure 5.1 Computational model building. In this example structural elements from the Hollandite structure (highlighted in (a)) are combined (b) to produce analogue structures. Once the structural elements have been reassembled in the appropriate form, a new unit cell can be defined (either automatically or by selecting translationally related atoms) (shown in (c)) and the symmetry of the new structure, constructed from regular and symmetrical elements, automatically determined (d) (in this case the new, enlarged, model is P42/m Hollandite itself is 141m). Once a new model is constructed its properties can be readily characterized as in (e) where the calculated X-ray powder diffraction pattern of one of many alternative Hollandite derivative structures is shown.

Nanoparticles with the hollandite structure can be prepared also from other transition-metal oxide phases, and it may be instructive at this point to compare these different systems. A recent report was made [191] on the synthesis and... 

FIGURE4.80 The Orthose (or hollandite) structure KAlSi O after Flint (1968) Penkala (1974) andUrusov (1987). 

FARRINGTON You identified K Hollandite as a conductor of K+ ions. I am not aware of any conclusive evidence that ions are actually conducted through the Hollandite structure under d.c. conditions. Our results Cl) reveal significant ion shifting at high frequencies but a d.c. ionic conductivity of < 10" cm between... 

The priderite structure is related to the hollandite structure and can give a singlephase product over a considerable range of stoichiometries near BaNiTiyOig. These Sb-free pigments were initially sold as heavy metal free pigments. 

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