Structural Features of the Modulated BiCu2(P1-xVx)O6 Solid Solution; 4-D Treatment of x = 0.87 Compoun
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- 作者：Olivier Mentré ; El Mostafa Ketatni ; Marie Colmont ; Marielle Huvé ; Francis Abraham ; Vaclav Petricek
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：August 23, 2006
- 年：2006
- 卷：128
- 期：33
- 页码：10857 - 10867
- 全文大小：497K
- 年卷期：v.128,no.33(August 23, 2006)
- ISSN：1520-5126
文摘
The BiCu2(P1-xVx)O6 system shows the appearance of various phenomena that progressivelychange as a function of the average (P/V)O4 groups size. Then, from x = 0 to x 
0.7, a solid solutionexists with respect to the basic orthorhombic unit cell of BiCu2PO6. For greater x values (0.7 < x <0.96),structural modulations with incommensurate q vector that slightly change versus x appear. The 4-D treatmentof single-crystal XRD data of the modulated phase corresponding to x = 0.87 at 100 K (orthorhombic, a =12.379(3)Å, b = 5.2344(9) Å, c = 7.8270(14) Å, q = 0.268(3) b*, super space group: Xbmm(0
0) s00, Xstands for the nonprimitive centering vector (1/2,0,1/2,1/2), R(obs)overall = 5.27%, R(obs)fundamental = 4.48%,R(obs)satellite = 6.58%) has evidenced strong positional modulated effects within the [BiCu2O2]3+ ribbonswhile three XO4 configurations compete along the x4 fourth dimension. There is no P/V segregation alongx4 in good agreement with steric-only origins of the modulation. Finally for 0.96 < x <1, two phases coexist,i.e., BiCu2VO6 (X = 1) and a modulated phase of the previous domain.The BiCu2VO6 crystal structureshows a unit cell tripling associated with monoclinic symmetry lowering. The VO4 orientations between tworibbons proceed with respect to the interribbon distance. Then the full system shows flexible interactionsbetween modulated Bi/M/O-based ribbons and surrounding tetrahedral groups, depending on the averageXO4 size. Furthermore, between two ribbons the Cu2+ arrangement forms magnetically isolated zigzagcopper two-leg ladders. Our preliminary results show a spin-gap behavior likely due to the existence oftrue S = 1/2 Heisenberg two-leg ladders. Modulated compositions are gapless, in good agreement withband-broadening toward a continuum in the magnetic excitation spectrum. The continuous distribution ofCu-Cu distances along the rungs and legs of the ladders should be mainly responsible for this magneticchange.
0.7, a solid solutionexists with respect to the basic orthorhombic unit cell of BiCu2PO6. For greater x values (0.7 < x <0.96),structural modulations with incommensurate q vector that slightly change versus x appear. The 4-D treatmentof single-crystal XRD data of the modulated phase corresponding to x = 0.87 at 100 K (orthorhombic, a =12.379(3)Å, b = 5.2344(9) Å, c = 7.8270(14) Å, q = 0.268(3) b*, super space group: Xbmm(00) s00, Xstands for the nonprimitive centering vector (1/2,0,1/2,1/2), R(obs)overall = 5.27%, R(obs)fundamental = 4.48%,R(obs)satellite = 6.58%) has evidenced strong positional modulated effects within the [BiCu2O2]3+ ribbonswhile three XO4 configurations compete along the x4 fourth dimension. There is no P/V segregation alongx4 in good agreement with steric-only origins of the modulation. Finally for 0.96 < x <1, two phases coexist,i.e., BiCu2VO6 (X = 1) and a modulated phase of the previous domain.The BiCu2VO6 crystal structureshows a unit cell tripling associated with monoclinic symmetry lowering. The VO4 orientations between tworibbons proceed with respect to the interribbon distance. Then the full system shows flexible interactionsbetween modulated Bi/M/O-based ribbons and surrounding tetrahedral groups, depending on the averageXO4 size. Furthermore, between two ribbons the Cu2+ arrangement forms magnetically isolated zigzagcopper two-leg ladders. Our preliminary results show a spin-gap behavior likely due to the existence oftrue S = 1/2 Heisenberg two-leg ladders. Modulated compositions are gapless, in good agreement withband-broadening toward a continuum in the magnetic excitation spectrum. The continuous distribution ofCu-Cu distances along the rungs and legs of the ladders should be mainly responsible for this magneticchange.