K_1+2xNi_1−xFe₂(AsO₄)₃(x= 0,125): un nouvel arséniate à structure de type α-CrPO₄

Abstract

A new arsenate K1 + 2xNi1 - xFe2(AsO4)3 (x = 1/8) was synthesized using a flux method and its crystal structure was determined from single-crystal X-ray diffraction data. It appears closely related to the α-CrPO4 structure type. The proposed structural model was validated by bond-valence-sum calculations, charge-distribution and Madelung energy analyses

An arsenate with the α-CrPO4structure type, NaCa1–xNi3–2xAl2x(AsO4)3(x= 0.23): crystal structure, charge-distribution and bond-valence-sum analyses

“…In our recent research (Ben Smail & Zid, 2017a), we have provided a brief review of -CrPO 4 structure-type compounds, including a discussion of the octahedral-site occupations in the covalent three-dimensional framework. Compared to these compounds, (I) features one of the octahedral sites occupied by a disordered distribution of di-and trivalent cations [0.54 (1) Ni 2+ + 0.46 (1) Al 3+ ] and the other by divalent cations (Ni 2+ ) [see Table 1 in Ben Smail & Zid (2017a)], and the sites within the tunnels also accommodate monovalent (Na + ) and divalent (Ca 2+ ) cations. This distribution is supported by the CHARDI and BVS results.…”

“…By labelling Q the computed charges, the q/Q ratio for the cations is the internal criterion for such an evaluation (Nespolo et al 1999). This model has been successfully used to validate numerous crystal structures (Ben Smail & Zid, 2017a;Nespolo et al, 2000Nespolo et al, , 2001Guesmi et al, 2006).…”

“…During our investigation of the A 2 O-NiO-X 2 O 5 (A = Na or Li; X = P and/or As) system, in search of new materials with open structures likely to exhibit interesting properties as electroactive materials, a number of new materials with various structures have been discovered, namely Na 4 Ni 7 -(AsO 4 ) 6 (Ben Smail et al, 2007), an arsenate exhibiting the -xenophyllite-like structure (Marzouki et al, 2013), Na 4 Ni 5 -[(As 0.73 ,P 0.27 )O 4 ] 2 [(As 0.59 ,P 1.41 )O 7 ] 2 (Ben Smail & Jouini, 2004), isostructural with the phosphate Na 4 Ni 5 (PO 4 ) 2 (P 2 O 7 ) 2 (Sanz et al, 1999), Na 3 Ni 2 (As 0.1 ,P 0.9 )O 4 (As 1.3 ,P 0.7 )O 7 and its limiting arsenate compound that is a moderate ionic conductor (Ben Smail & Jouini, 2005), NaNi 4 (AsO 4 ) 3 , the first noncentrosymmetric nickel arsenate (Ben Smail et al, 2002), and LiNi 2 As 3 O 10 , which is the first nickel triarsenate with a tunnel structure (Ben Smail & Zid, 2017b). Recently, we have extended our study to the quaternary A 2 O-Fe 2 O 3 -NiO-As 2 O 5 system (A = alkali metal), in which we have synthesized a new arsenate with the -CrPO 4 structure type (Glaum et al, 1986;Attfield et al, 1988), namely K 1.25 Ni 0.875 Fe 2 (AsO 4 ) 3 (Ben Smail & Zid, 2017a).…”

Structural and Spectroscopic Studies of NaCuCr2(PO4)3: A Noncentrosymmetric Phosphate Belonging to the α-CrPO4-Type Compounds

“…They are identified with the general chemical formula □ 3 M 3 (XO 4 ) 3 , where □ is a vacancy that can be filled by monovalent and/or divalent cations, introducing an oxidation state decrease of the transition metal M and XO 4 referring to tetrahedral entity, respectively. They all crystallize with a centrosymmetric Imma space group. − Interestingly, some of them with the following general formula A 2 M 2+ 2 M 3+ (PO 4 ) 3 , where A is an alkali and M are metals able to show an oxidation equal to 2 and/or 3, were recently described as low-temperature polymorphs of the alluaudite-type structure. , …”