Die Kristallstruktur der ferroischen Verbindung Pb3[O|GeO4]

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Abstract
Light yellow single crystals of Pb3[O|GeO4], a ferroelastic and possibly antiferroelectric compound, were grown from melt by spontaneous crystallization. The crystal data are a = 5.260(1), b = 10.437(2), c = 5.477(1) Å, and β = 92.55(3)°; space group P2l; D obs = 8.52(5), Dx = 8.560 g · cm−3 for Z = 2. X-ray powder data are given. The crystal structure has been determined by means of 1464 unique reflections, collected with an automated 4-circle diffractometer using Mo Kα radiation. The final R value was 0.075. The comparatively simple crystal structure consists of isolated [GeO4]4− tetrahedra connected by three non-equivalent Pb atoms with similarly pyramidal arrangement of four nearest oxygen neighbours at distances below 2.71 Å. The dipol moments of the Pb polyhedra point to channels extending parallel to [001]. In addition one oxygen atom O(5) occupies an octahedral hole between the Pb atoms laying out of center covalently bonded to three of them by short bonds of 2.159, 2.268 and 2.323 Å in length. The Ge —O tetrahedral distances range from 1.728 to 1.789 Å. Prominent ferroelastic (100) domain walls in the twinned crystals correspond structurally to an axial b glide plane.

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