Syntheses, Structural Analyses, and Unusual Magnetic Properties of Ba2CoSi2O7 and BaCo2Si2O7
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- 作者：Richard D. Adams ; Christophe Payen ; Timir Datta ; Lars Ö ; hrströ ; m ; and Ralph Layland
- 刊名：Inorganic Chemistry
- 出版年：1996
- 出版时间：June 5, 1996
- 年：1996
- 卷：35
- 期：12
- 页码：3492 - 3497
- 全文大小：219K
- 年卷期：v.35,no.12(June 5, 1996)
- ISSN：1520-510X
文摘
The compounds Ba2CoSi2O7,1, and BaCo2Si2O7,2, were obtained by heating mixtures of BaCO3,CoCO3, andSiO2 in the proper stoichiometries to 1300 
C for 48 h.Both materials were characterized by single-crystalX-ray diffraction and magnetization measurements on powder andpartially oriented single crystals. Each cobaltion in 1 is surrounded by four oxygen atoms derived from the[Si2O7]6- groups inthe form of a distorted tetrahedron.The cobalt ions are bridged by O-Si-O and O-Si-O-Si-Ogroups from the[Si2O7]6- ions inan extendedtwo-dimensional arrangement. The barium ions are arranged inlayers that run parallel to theCo[Si2O7] layers.In 2 each cobalt ion is also surrounded by anarrangement of four oxygen atoms derived from theSi2O7 groupsin a distorted tetrahedral shape. These tetrahedra are linked intochains through the sharing of one of the oxygenatoms from the Si2O7 groups. TheCoO4 chains are crosslinked via O-Si-O-Si-O bridgesfrom the Si2O7groups. The barium ions occupy channels that run parallel to thecrystallographic c-axis. Curie-Weissbehaviorsand temperature independent paramagnetisms (TIP) coexist in the ranges40-300 K and 100-300 K for 1 and2, respectively. For both compounds the values of theCurie constant and TIP are consistent with tetrahedralCo(II) ions having three unpaired electrons. While compound1 remains paramagnetic down to 5 K, 2undergoesa transition into a state having a field-induced weak ferromagneticresponse at Tc = 21 K. The weakferromagneticproperties below Tc can be explained by spincanting and spontaneous domain formation. The canting angleisestimated to be about 5 at 5 K. Interestingly, 2could represent the first example among the tetrahedralCo(II)compounds with the transition temperature (Tc= 21 K) being higher than the zero-field splitting of the4A2electronic ground state. Crystal data: for 1, formulaBa2CoSi2O7, a =8.450(1) Å, b = 10.729(1) Å, c =8.474(1) Å, 
= 111.365(8), monoclinic, space group =C2/c, Z = 4; for 2,formula BaCo2Si2O7,a = 7.2131(6) Å,b = 12.781(1) Å, c = 13.762(1) Å, = 90.299(8), monoclinic, space group =C2/c, Z = 8.
C for 48 h.Both materials were characterized by single-crystalX-ray diffraction and magnetization measurements on powder andpartially oriented single crystals. Each cobaltion in 1 is surrounded by four oxygen atoms derived from the[Si2O7]6- groups inthe form of a distorted tetrahedron.The cobalt ions are bridged by O-Si-O and O-Si-O-Si-Ogroups from the[Si2O7]6- ions inan extendedtwo-dimensional arrangement. The barium ions are arranged inlayers that run parallel to theCo[Si2O7] layers.In 2 each cobalt ion is also surrounded by anarrangement of four oxygen atoms derived from theSi2O7 groupsin a distorted tetrahedral shape. These tetrahedra are linked intochains through the sharing of one of the oxygenatoms from the Si2O7 groups. TheCoO4 chains are crosslinked via O-Si-O-Si-O bridgesfrom the Si2O7groups. The barium ions occupy channels that run parallel to thecrystallographic c-axis. Curie-Weissbehaviorsand temperature independent paramagnetisms (TIP) coexist in the ranges40-300 K and 100-300 K for 1 and2, respectively. For both compounds the values of theCurie constant and TIP are consistent with tetrahedralCo(II) ions having three unpaired electrons. While compound1 remains paramagnetic down to 5 K, 2undergoesa transition into a state having a field-induced weak ferromagneticresponse at Tc = 21 K. The weakferromagneticproperties below Tc can be explained by spincanting and spontaneous domain formation. The canting angleisestimated to be about 5 at 5 K. Interestingly, 2could represent the first example among the tetrahedralCo(II)compounds with the transition temperature (Tc= 21 K) being higher than the zero-field splitting of the4A2electronic ground state. Crystal data: for 1, formulaBa2CoSi2O7, a =8.450(1) Å, b = 10.729(1) Å, c =8.474(1) Å, = 111.365(8), monoclinic, space group =C2/c, Z = 4; for 2,formula BaCo2Si2O7,a = 7.2131(6) Å,b = 12.781(1) Å, c = 13.762(1) Å, = 90.299(8), monoclinic, space group =C2/c, Z = 8.