Structures, lattice rutile

The structure of titanium complexes affects the formation of hydrated titanium dioxide structure, since rutile and anatase lattices are composed of TiO octahedrons connected in definite manner. The formation of anatase structure occurs when two octahedral complexes form a common vertex. When two octahedrons are united via their edges, rutile structure is formed. Based on this assumption, it is considered that if titanium (IV) complexes with one reactive centre are formed during hydrolysis, anatase structure is formed if there are two reactive centres, then rutile structure is formed. 

In203 has the C-type M2O3 structure (p. 1238) and InO(OH) (prepared hydrothermal ly from In(OH)3 at 250-400°C and 100-1500 atm) has a deformed rutile structure (p. 961) rather than the layer lattice structure of AIO(OH) and GaO(OH). Crystalline In(OH)3 is best prepared by addition of NH3 to aqueous InCl3 at 100° and ageing the precipitate for a few hours at this temperature it has the simple Re03-type structure distorted somewhat by multiple H bonds. 

NakayamaS however, has suggested that, for rutile, which is tetragonal in structure, the strong bond between metal and oxide results from the favourable spacing between titanium ions in the rutile lattice and those in the metal structure. This explanation, however, does not account for the fact that other oxides of titanium, such as brookite, which is orthorhombic, and anatase, which is tetragonal, are also protective . 

The interstitial hydrides of transition metals differ from the salt-like hydrides of the alkali and alkaline-earth metals MH and MH2, as can be seen from their densities. While the latter have higher densities than the metals, the transition metal hydrides have expanded metal lattices. Furthermore, the transition metal hydrides exhibit metallic luster and are semiconducting. Alkali metal hydrides have NaCl structure MgH2 has rutile structure. 

M-M multiple bonding has long been known in metal oxide structures. The first Mo=Mo bond was seen in one crystalline form of Mo02 which has a distorted rutile structure wherein the Mo(4+) ions occupy adjacent octahedral holes throughout the lattice ( 4). The octahedra are distorted because of the short Mo-Mo distances 2.51 X. La. RejO has a fluorite type structure in which 02 is substituted for F and four of the five Ca2 sites are occupied by La3 ions. The remaining Ca2 site is occupied by an (Re=Re)8 unit with an Re-Re distance 2.259(1) A... 

Technical electrodes usually consist of a mixture of Ru02 and TiC>2 plus a few additives. They are called dimensionally stable anodes because they do not corrode during the process, which was a problem with older materials. These two substances have the same rutile structure with similar lattice constants, but RuC>2 shows metallic conductivity, while pure TiCU is an insulator. The reaction mechanism on these electrodes has not yet been established the experimental results are not compatible with either of the two mechanisms discussed above [4]. 

Table 2.1 shows the crystal structure data of the phases existing in the Mg-H system. Pnre Mg has a hexagonal crystal structure and its hydride has a tetragonal lattice nnit cell (rutile type). The low-pressure MgH is commonly designated as P-MgH in order to differentiate it from its high-pressure polymorph, which will be discussed later. Figure 2.2 shows the crystal structure of p-MgH where the positions of Mg and H atoms are clearly discerned. Precise measurements of the lattice parameters of p-MgH by synchrotron X-ray diffraction yielded a = 0.45180(6) mn and c = 0.30211(4) nm [2]. The powder diffraction file JCPDS 12-0697 lists a = 0.4517 nm and c = 0.30205 nm. The density of MgH is 1.45 g/cm [3]. 

Studies of the V20a-V204 system have confirmed that the phases V 02 i ( = 2—9) exist below 1400°C. ° The crystal structure of V4O7 has been shown to be based on the rutile lattice, the VOg octahedra being considerably distorted with V—O = 178—212 pm. The heat and entropy of formation of Vj Ojj at 1333 K have been determined as —373 kJmol and 146Jmol K respectively, by electrochemical measurements. ... 

The lattice constants of the fluorides of the rutile type, the x-ray work on which is owing to Stout and Reed 306) and Baur 23, 24, 25) are listed in the following Table 29. Finally Bartlett and Maitland 19) reported the rutile structure for PdFg also. 

It has been shown earlier that the parameters of the rutile structure can be very simply derived by setting the Ti-O bond lengths to the value expected for octahedral coordination (1.95 A) and then allowing the structure to relax to maximum volume. There are three parameters the lattice parameters a and c and a parameters characterising the oxygen positions. The calculated values are (observed in parentheses)... 

Compounds of stoichiometry AX2 with six-coordinated A require (according to eqn (11.1)) that X be three coordinate. Since none of the close packed lattices have cage points with three coordination, these structures are less simple. The rutile (202240) and anatase (202242) forms of Ti02 are based on FICP and FCC lattices of Ti respectively, but fitting the ions into positions of three coordination results in distortions that lower the symmetry. An alternative derivation of these structures is described in Section 11.2.2.4 below. 

A structure model was proposed for the compounds with Dj-type patterns by Bursill and Hyde. Figure 2.112 shows a reciprocal lattice plane of rutile with a [111] zone axis. The arrays of superspots for Dj and Dj patterns are parallel to the vectors g(121) and g(l 32), respectively. Those for D2 patterns... 

Fig. 2.112 Reciprocal lattice plane of rutile-typc structure with [111] zone axis. The (s, t) series of shear planes are indicated by dashed lines (see text). White circles are the possible shear planes for this system.

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