The novel borate Lu₅Ba₆B₉O₂₇with a new structure type: synthesis, disordered crystal structure and negative linear thermal expansion

Abstract

Edited by R. Č erný, University of Geneva, SwitzerlandKeywords: lutetium barium borate; crystal structure; negative thermal expansion (NTE); high-temperature X-ray powder diffraction (HTXRD). CCDC reference: 1917796Supporting information: this article has supporting information at journals.iucr.org/bThe novel borate Lu 5 Ba 6 B 9 O 27 with a new structure type: synthesis, disordered crystal structure and negative linear thermal expansion Single crystals of Lu 5 Ba 6 B 9 O 27 were obtained by cooling from a melt and polycrystals of the borate were prepared using a multi-step solid-state synthesis. The crystal structure was determined from single-crystal X-ray diffraction data. The borate crystallizes in a new structure type in the monoclinic crystal system in space group C2/c, with cell parameters a = 13.0927 (3), b = 9.9970 (2) and c = 20.4884 (4) Å , = 106.827 (1) , V = 2566.86 (9) Å 3 and Z = 4. It is described as a framework composed of rings consisting of vertex-sharing [BO 3 ] triangles and [LuO 6 ] octahedra. The Ba atoms are in the cavities of the framework. The structure is disordered: one of the B atoms is surrounded by six O atoms with partial occupancies of 0.5. The thermal properties of Lu 5 Ba 6 B 9 O 27 were investigated by thermal analysis and high-temperature X-ray powder diffraction. Its thermal expansion is highly anisotropic. The negative expansion (contraction) is along the b axis, i.e. parallel to the planes of the largest number of [BO 3 ] triangles. The coefficient of negative linear expansion ranges from À1.42 (at 20 C) to À5.57 Â 10 -6 C -1 (at 1000 C). Thermal deformation of the ac plane is described in terms of the theory of shear deformation of monoclinic crystals. The Lu 5 Ba 6 B 9 O 27 sample melts at 1170 C.

Novel “Anti-Zeolite” Ba3Sr3B4O12: Eu3+ Phosphors: Crystal Structure, Optical Properties, and Photoluminescence

“…The difference between crystal structures is the different configuration of the disordered BO3 triangles in the channels along the c axis (Figure 5). Except for the "anti-zeolite" family, similar coordination of B-O environments has also been found in Ln14(GeO4)2(BO3)6O8 (Ln = Nd, Sm) [35], Li2Rb7Sr24(BO3)19 [36], Lu5Ba6(BO3)9 [37], Pb2(BO3)(NO3) [38], and Rb9Ba24(BO3)19 [39].…”

Ba3(BO3)2: the first example of dynamic disorder in a borate crystal

“…Following the hypothesis according to which the observed, in experiments, static disorder of oxygen atoms around fixed (with the full occupancy) boron atoms is the result of the quenching of the dynamically disordered phase, the Lu 5 Ba 6 B 9 O 27 24 crystal can be suggested as the next candidate for which the dynamically disordered state can be observed at high temperatures. Structures with such a crystal-chemical feature are rare among borates.…”

“…Structures with such a crystal-chemical feature are rare among borates. In the work of Filatov et al , 24 the Lu 5 Ba 6 B 9 O 27 structure is characterized as the first structure with statically disordered oxygen around a fixed boron atom. However, by analogy with carbonate, the presence of static disorder is not an obligatory requirement for the existence of a high-temperature disordered state, and there may also be a number of borates for which this structural phenomenon will be detected.…”