Lead ferroniobate PbFe 1 / 2 Nb 1 / 2 O 3 (PFN) also belongs to the family of ferroelectromagnets with perovskite structure and exhibits ferroelectric and antiferromagnetic properties. Sergey Ivanov, in Science and Technology of Atomic, Molecular, Condensed Matter & Biological Systems, 2012 6.1 Pb ( Fe 1 / 2 B 1 / 2 ) O 3 perovskites The second neighbor shell is occupied by hydrogen atoms at a distance of 1.63 Å, while chlorine atoms form the third neighbor shell at 2.32 Å. The first neighbors of hydrogen are nitrogen atoms at a distance of 1.03 Å. considerably lower than the crystallographic symmetry. However, the hydrogen atoms do not occupy high symmetry positions, and therefore, the holographic symmetry of the arrangement of atoms as viewed by a hydrogen probe nucleus is only simple cubic, i.e. The tetrahedra can adopt two distinct symmetrical orientations, which are randomly distributed with equal probability at room temperature ( Fig. Four hydrogen atoms are at the vertices of a tetrahedron surrounding each nitrogen atom thereby forming an ammonium ion. The crystal lattice resembles a CsCl structure in that a nitrogen atom is surrounded by eight atoms of chlorine. In spite of its relatively simple structure, ammonium chloride (NH 4Cl) constitutes an interesting test case for atomic resolution neutron holography. This example demonstrates the ability and power of Mössbauer spectroscopy in site determination. This theory is nicely reflected in the experimental results. The subspectra areas should behave like Fe-I : Fe-IIa : Fe-IIb = 1 : 2 : 1, because 25% of the iron atoms are located at the corners, and Fe-IIa : Fe-IIb = 50% : 25% because four Fe-atoms at the face centers have θ = 0 and only two have θ = 90° . This exactly matches the experimental findings in Table 2. From eqn, it follows that the magnitude of E q for the Fe-IIb site is twice as large as that for the Fe-IIa site but of opposite sign. For both cases, the asymmetry parameter is η = 0 and V zz is identical. For the site Fe-IIb, EFG and z-axis are perpendicular, that is, θ = 90°. Thus, one has to distinguish two cases for the Fe-II site: for site Fe-IIa, the main component V zz is collinear with the hyperfine field B hf, that is, theta = 0. There is no electric field gradient for the Fe-I site, but one for the Fe-II site having nitrogen neighbors. The magnetic easy axis is the (1 0 0) direction, which is indicated by the z-axis in Figure 11. material is ferromagnetic with a Curie temperature of T C = 767 K, that is, well above the measurement temperature, which in this case is the room temperature. IS – isomer shift, QS – quadrupole splitting, BHF – hyperfine field, LW – line width, RA – relative area.
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