Preparation and structure of a ternary oxide of barium and rhenium, Ba3Re2-xO9

Abstract

Attempts to synthesize-BaRe03 resulted in formation of a slightly nonstoichiometric compound with the ideal formula Ba3Re209. It was found to have the space group R h with hexagonal unit cell parameters a = 5.7699 ( 5 ) A and c = 20.799 (2) A, Z = 3. A total of 2816 reflections were measured on an automatic diffractometer, and the structure was refined by full-matrix least squares on 308 unique reflections to a final R value of 0.027 and R, of 0.036. It consists of a nine-layer repeat sequence of hexagonal and cubic close-packed layers of composition BaO,. The stacking of these layers along the c axis leads to the formation of two types of octahedral sites, M(1) and M(2), for the Re atoms. An M(2) octahedron shares opposite faces with two M( 1) octahedra. Site population analysis has shown that about 8% of the M(2) sites are occupied and that simultaneous occupation of two octahedral sites sharing a face is avoided, resulting in the Re deficient compound Ba3Rei,9,09. All the Ba atoms are 12-coordinated and both Reo, octahedra show a distortion corresponding to an elongation along the trigonal axis. IntroductionA large number of ternary oxides AMO,, where A is a large cation and M is a transition-metal cation, crystallize in the

Intergrowth polytypoids as modulated structures: the example of the cation deficient oxides LaTi1-xO3

“…In the current LaTi 1Àx O 3 case, the upper limit for g L of 5 = 12 for La 4 Ti 3 O 12 is set not by this rather steric limit but by the maximal allowed valence of Ti in charge balance considerations. In closely related phases, however, where ions of differing charge can apparently occupy the various cation sites (see [1] for examples) it may be possible to obtain a phase with a higher value for g L than 5 = 12 , and in fact the sequence and the g L value corresponding to x 1 = 3 has been observed [14].…”

High-pressure synthesis and crystal structure of the strontium tungstate Sr3W2O9

“…Some compounds with the chemical formula A 3 &M 2 X 9 (& = vacancy) have a Ba 3 Re 2 O 9 -type structure, which is regarded as a layered perovskite structure (Calvo et al, 1977). The present authors have reported a barium tungstate, Ba 3 W 2 O 9 , with the Ba 3 Re 2 O 9 -type structure, which was prepared by a highpressure synthesis technique (Urushihara et al, 2017).…”

Crystal chemical simulation of superconductors on the basis of oxide and intermetallic layers

“…In the homologous series of these compounds, just like in the AB 2 C 2 (ThCr 2 Si 2 -and CaBe 2 Ge 2 -type) compounds series, the value of a parameter varies, as a rule, proportionally to variation of A, B and C atoms sizes. Furthermore, in [53], Nb [54 -56], Ta [57 -59], Re [60], Ru [61] and Ti [62] would be approximately equal to average bond lengths in В'О 6 octahedra of respective elements and fall into the range 1.90-2.00 Å (the limit of stability of B'-O bonds in these elements octahedra is rather wide (1.70-2.30 Å)). Therefore, the elementary unit parameter a and the distances B-B or C-C in the B 2 C 2 -sandwich internal plane would be in the range 3.80-4.00 Å and 2.76-2.83 Å, respectively.…”