Tetragonal elementary cell

The c-axis (z-axis) view of the tetragonal elementary cell with the respective ground-state orbitals of the central atom is provided in the top part of Fig. 1. Only upper lobes of the xz and yz orbitals, above the equatorial plane (above the ab plane, xy plane), are shown. The ones beneath the ab plane have the same shape but opposite sign. 

Fig. 5 Antiferrodistortive ordering of tetragonal elementary cells with rhombic JT instabdity of E b g type (z axis view of the ay plane), (a) The case when elementary cells do not share common atoms, (b) Same when elementary cells share common vertices. (From [16,17])...

Fig. 6 Antiferrodistortive order of tetragonal elementary cells with rhombic JT instability of the E b g type (similar to Fig. 3b). (a) In the traditional approach, ligands are explicitly included. Orientation of central-atom orbitals is determined by formation of chemical bonds with nearest-neighbor ligands, (b) In the OOA ligands are omitted. Central-atom orbitals point toward next-neighbor sites...

P-Pb02 crystals have a tetragonal elementary cell of the rutile type with axes a = 4.945 A b = 3.378 A... 

The AI3 (Sc, Ti, V, Cr) series of trialuminides crystallize in the cubic II2 (Figure 10.2) and tetragonal DO22 structure. The tetragonal elementary cell of DO22... 

Boron nitride is a voluminous white powder which under the microscope shows no sign of crystallization. The sp. gr. depends on the temp, to which it has been ignited. F. M. Jager and H. G. K. Westenbrink said that the X-radiogram shows that the space-lattice is either cubic with a=7 44 A., or tetragonal with o=4 295 A., and c—5 176 A., or a c= 1 1 2052. In the first case, the elementary cell contains 20 molecules, which is improbable and in the second case, 4 or 5... 

At relatively high temperature, the elastic intercell coupling is averaged out. Therefore, at different elementary cells, geometric shapes and amplitudes of the JT distortions are independently random. In other words, there is some distortion-magnitude disorder in the crystal lattice. At average, the respective X-ray crystal structure looks perfectly tetragonal. 

Red lead crystallizes as a tetragonal system and its elementary cell parameters are a = 8.80 A, c = 6.56 A. Figure 5.2 illustrates the coordination of ions in Pb304 crystal lattice. The latter... 

Fig. 4.2. Elementary crystal cell (a) cubic configuration and (b) tetragonal configuration due to polarization along the es-direction.

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