The Lengjiaxi and Banxi groups of the Meso-Neoproterozoic and the Lower Paleozoic along the profile at Huangtudian-Xianxi of the central-northern Hunan Province, China underwent very low-grade metamorphism. Illite cry...The Lengjiaxi and Banxi groups of the Meso-Neoproterozoic and the Lower Paleozoic along the profile at Huangtudian-Xianxi of the central-northern Hunan Province, China underwent very low-grade metamorphism. Illite crystallinity (IC) data of the <2 μm fractions range from 0.18-0.21°Δ2θ for the Lengjiaxi Group to 0.19–0.23°Δ2θ for the Banxi Group to 0.20–0.29°Δ2θ for the Sinian to the Lower Paleozoic (Kübler index, corrected with Kisch IC set, 1991). This indicates that the metamorphic grade of the Lengjiaxi Group is in the epizone, the Banxi Group in the epizone-high anchizone, and the Sinian to the Lower Paleozoic mostly in the high anchizone along the profile investigated. The peak metamorphic temperature evaluated is roughly 340–240°C. This result does not agree with the greenschist or subgreenschist facies of the Lengjiaxi and Banxi groups and neither with the lower-greenschist facies or diagenitic zone of the Sinian to the Lower Paleozoic, of which most previous researchers thought. The illites (K-mica) b 0 values range from 0.8989–0.9050 nm for the Lengjiaxi Group to 0.8984–0.9037 nm for the Banxi Group to the Lower Paleozoic. Based on the cumulative frequency curves of illite (K-mica) b 0, the peak metamorphic pressure of the Banxi Group to the Lower Paleozoic along the profile was derived in a low-intermediate pressure type. Illites occur as 2M1 polytype in the Lengjiaxi and Banxi groups and as 2M1+1 M types in some samples of the Lower Paleozoic. This indicates that the transformation of illite polytype from 1M to 2M1 was fulfilled within the high anchizone.展开更多
Silicon carbides are basilic ceramics with proper bandgaps （2.4-3.3 eV） and unique optical properties. SiC@C monocrystal nanocapsules with different morphologies, sizes, and crystal types were synthesized via the fa...Silicon carbides are basilic ceramics with proper bandgaps （2.4-3.3 eV） and unique optical properties. SiC@C monocrystal nanocapsules with different morphologies, sizes, and crystal types were synthesized via the fast and facile direct current （DC） arc discharge plasma method. The influence of Ar atmosphere on the formation of nanocrystal SiC polytypes was investigated by optical emission spectroscopy （OES） diagnoses on the arc discharge plasma. Boltzmann＇s plot was used to estimate the temperatures of plasma containing different Ar concentrations as 10,582 K （in 2 × 10^4 Pa of Ar partial pressure） and 14,523 K （in 4 × 10^4 Pa of Ar partial pressure）. It was found that higher energy state of plasma favors the ionization of carbon atoms and promotes the formation of α-SiC, while β-SiC is generally coexistent. Heat-treatment in air was applied to remove the carbon species in as-prepared SiC nanopowders. Thus, the intrinsic characters of SiC polytypes reappeared in the ultraviolet-visible （UV-vis） light absorbance. It was experimentally revealed that the direct bandgap of SiC is 5.72 eV, the indirect bandgap of β-SiC （3C） is 3.13 eV, and the indirect bandgap of α-SiC （6H） is 3.32 eV; visible quantum confinement effect is predicted for these polytypic SiC nanocrystals.展开更多
Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes.This paper presents the first authigenic illite K-Ar a...Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes.This paper presents the first authigenic illite K-Ar age data from fault gouge samples collected from the Red River Shear Zone at Lao Cai province,Vietnam.The fault gouge samples were separated into three grain-size fractions（〈0.1 μm,0.1-0.4 μm and 0.4-1.0 μm）.The results show that the K-Ar age values decrease from coarser to finer grain fractions（24.1 to 19.2 Ma）,suggesting enrichment in finer fraction of morerecently grown authigenic illites.The timing of the fault movement are the lower intercept ages at 0%detrital illite（19.2 ± 0.92 Ma and 19.4 ± 0.49 Ma）.In combination with previous geochronological data,this result indicates that the metamorphism of the Day Nui Con Voi（DNCV） metamorphic complex took place before ca.26.8 Ma.At about 26.8 Ma-25 Ma,the fault strongly acted to cause the rapid exhumation of the rocks along the Red River-Ailoa Shan Fault Zone（RR-ASFZ）.During brittle deformation,the DNCV slowly uplifted,implying weak movement of the fault.This brittle deformation might have lasted for ca.5 Ma.展开更多
There is a type of complex oxide mineral, composed of many elements such as Sn, Mg, Fe, Zn, Ti, Mn, Al, etc., in the areas of Anhua, Linwu and Shizhuyuan of Hunan Province. These minerals belong to nigerite, Mg-nigeri...There is a type of complex oxide mineral, composed of many elements such as Sn, Mg, Fe, Zn, Ti, Mn, Al, etc., in the areas of Anhua, Linwu and Shizhuyuan of Hunan Province. These minerals belong to nigerite, Mg-nigerite (pengzhizhongite), etc.. According to the principle of closest packing, the crystal chemical properties of nigerite (brown), pengzhizhongite (buff), Zn-nigerite (fawn), Fe-nigerite, Mn-nigerite (greenish-black) etc. have been analyzed. Their crystal structures may be characterized by O (the layers of cation octahedral coordinations), T_1 (the mixed layers of cation octahedral coordinations and cation tetrahedral coordinations in same directions), T_2 (the mixed layers of cation octahedral coordinations and cation tetrahedral coordination in different directions). The position of layer-O and layer-T is alternate permutation. The crystal structure of pengzhizhongite (6 H ) may be expressed by …OT_2OT_1OT_1…, taaffeite (8 H ), …OT_2OT_1OT_2OT_1…, and nigerite (24 R ), … OT_1OT_2 OT_2OT_1 …×3 etc.. In their structure, there are not only the crystal structure units of spinel … OT_2 OT_2 … but also the units of nolanite … OT_1 OT_1 …. The research of these minerals has important theoretic and practical significance in the fields of minerals, gemology, material science etc..展开更多
The domain structures in calcium-cerium fluorocarbonate mineral series from a rare earth mineral deposit within an aegirine alkali granite massif in Mianning County, Sichuan Province, China, were studied by means of t...The domain structures in calcium-cerium fluorocarbonate mineral series from a rare earth mineral deposit within an aegirine alkali granite massif in Mianning County, Sichuan Province, China, were studied by means of transmission electron microscopy. Many categories of domain structures in this mineral series were observed and investigated, including the microtwin domains of parisite-6R(2) and B2S-6R, the antiphase domains of B2S-2H. The results show that the antiphase domains which are faults along crystal plane (0001) are formed by the displacement of crystal lattice in c * direction and the displacement is 0.471 nm. A new polytype (B4S2-3R) of regular mixed-layer structure with B4S2 type is found in the domain region of mixed-layer structure.展开更多
In-situ formation fibrous polytype AlN composite ceramic materials was prepared from AlN-Y_2O_3-SiO_2 system.In comparison with AlN ceramics,both bending strength and fracture toughness of the composite materials are ...In-situ formation fibrous polytype AlN composite ceramic materials was prepared from AlN-Y_2O_3-SiO_2 system.In comparison with AlN ceramics,both bending strength and fracture toughness of the composite materials are much bettered.Microstructural observation revealed that a lot of epitaxial growth fibrous AlN polytype occurred in matrix.Y_2O_3 seems to act as a densifier for in-situ formation materials and as medium for growth of fibrous polytype.SiO_2 is the growth promoter for fibrous polytype.The occurrnce of fibrous polytype may increase the strength and toughness of AlN ceramic composite mateirals.展开更多
The resistivities of vanadium-doped semi-insulating 4H-SiC wafers were measured by a contactless resistivity measurement system. Anomalous resistivity was found in semi-insulating 4H-SiC wafer. Raman spectra of semi-i...The resistivities of vanadium-doped semi-insulating 4H-SiC wafers were measured by a contactless resistivity measurement system. Anomalous resistivity was found in semi-insulating 4H-SiC wafer. Raman spectra of semi-insulating4H-SiC wafer indicated that the anomalous resistivity was caused by polytype inclusion. Based on the activation energies of different SiC polytypes calculated from resistivity versus temperature data measured by COREMA-VT, the resistivities in the vanadium-doped semi-insulating 4H-SiC wafer with 6H polytype inclusion were calculated. The calculated resistivities are quite consistent with the measured resistivities. Furthermore, the compensation mechanism for the formation of anomalous resistivity was proposed.展开更多
基金This work was suppored by the National Natural Science Foundaition of China(Grant No.49872033).
文摘The Lengjiaxi and Banxi groups of the Meso-Neoproterozoic and the Lower Paleozoic along the profile at Huangtudian-Xianxi of the central-northern Hunan Province, China underwent very low-grade metamorphism. Illite crystallinity (IC) data of the <2 μm fractions range from 0.18-0.21°Δ2θ for the Lengjiaxi Group to 0.19–0.23°Δ2θ for the Banxi Group to 0.20–0.29°Δ2θ for the Sinian to the Lower Paleozoic (Kübler index, corrected with Kisch IC set, 1991). This indicates that the metamorphic grade of the Lengjiaxi Group is in the epizone, the Banxi Group in the epizone-high anchizone, and the Sinian to the Lower Paleozoic mostly in the high anchizone along the profile investigated. The peak metamorphic temperature evaluated is roughly 340–240°C. This result does not agree with the greenschist or subgreenschist facies of the Lengjiaxi and Banxi groups and neither with the lower-greenschist facies or diagenitic zone of the Sinian to the Lower Paleozoic, of which most previous researchers thought. The illites (K-mica) b 0 values range from 0.8989–0.9050 nm for the Lengjiaxi Group to 0.8984–0.9037 nm for the Banxi Group to the Lower Paleozoic. Based on the cumulative frequency curves of illite (K-mica) b 0, the peak metamorphic pressure of the Banxi Group to the Lower Paleozoic along the profile was derived in a low-intermediate pressure type. Illites occur as 2M1 polytype in the Lengjiaxi and Banxi groups and as 2M1+1 M types in some samples of the Lower Paleozoic. This indicates that the transformation of illite polytype from 1M to 2M1 was fulfilled within the high anchizone.
基金This work was financially supported by the National Natural Science Foundations of China （Nos. 51331006 and 51271044）.
文摘Silicon carbides are basilic ceramics with proper bandgaps （2.4-3.3 eV） and unique optical properties. SiC@C monocrystal nanocapsules with different morphologies, sizes, and crystal types were synthesized via the fast and facile direct current （DC） arc discharge plasma method. The influence of Ar atmosphere on the formation of nanocrystal SiC polytypes was investigated by optical emission spectroscopy （OES） diagnoses on the arc discharge plasma. Boltzmann＇s plot was used to estimate the temperatures of plasma containing different Ar concentrations as 10,582 K （in 2 × 10^4 Pa of Ar partial pressure） and 14,523 K （in 4 × 10^4 Pa of Ar partial pressure）. It was found that higher energy state of plasma favors the ionization of carbon atoms and promotes the formation of α-SiC, while β-SiC is generally coexistent. Heat-treatment in air was applied to remove the carbon species in as-prepared SiC nanopowders. Thus, the intrinsic characters of SiC polytypes reappeared in the ultraviolet-visible （UV-vis） light absorbance. It was experimentally revealed that the direct bandgap of SiC is 5.72 eV, the indirect bandgap of β-SiC （3C） is 3.13 eV, and the indirect bandgap of α-SiC （6H） is 3.32 eV; visible quantum confinement effect is predicted for these polytypic SiC nanocrystals.
基金financially supported by the Vietnam National Foundation for Science and Technology Development(NAFOSTED) under grant number 105.032011.11 to Bui Hoang Bac
文摘Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes.This paper presents the first authigenic illite K-Ar age data from fault gouge samples collected from the Red River Shear Zone at Lao Cai province,Vietnam.The fault gouge samples were separated into three grain-size fractions（〈0.1 μm,0.1-0.4 μm and 0.4-1.0 μm）.The results show that the K-Ar age values decrease from coarser to finer grain fractions（24.1 to 19.2 Ma）,suggesting enrichment in finer fraction of morerecently grown authigenic illites.The timing of the fault movement are the lower intercept ages at 0%detrital illite（19.2 ± 0.92 Ma and 19.4 ± 0.49 Ma）.In combination with previous geochronological data,this result indicates that the metamorphism of the Day Nui Con Voi（DNCV） metamorphic complex took place before ca.26.8 Ma.At about 26.8 Ma-25 Ma,the fault strongly acted to cause the rapid exhumation of the rocks along the Red River-Ailoa Shan Fault Zone（RR-ASFZ）.During brittle deformation,the DNCV slowly uplifted,implying weak movement of the fault.This brittle deformation might have lasted for ca.5 Ma.
基金ThispaperissupportedbytheNationalNaturalScienceFoundationofChina (No .492 72 0 91 )
文摘There is a type of complex oxide mineral, composed of many elements such as Sn, Mg, Fe, Zn, Ti, Mn, Al, etc., in the areas of Anhua, Linwu and Shizhuyuan of Hunan Province. These minerals belong to nigerite, Mg-nigerite (pengzhizhongite), etc.. According to the principle of closest packing, the crystal chemical properties of nigerite (brown), pengzhizhongite (buff), Zn-nigerite (fawn), Fe-nigerite, Mn-nigerite (greenish-black) etc. have been analyzed. Their crystal structures may be characterized by O (the layers of cation octahedral coordinations), T_1 (the mixed layers of cation octahedral coordinations and cation tetrahedral coordinations in same directions), T_2 (the mixed layers of cation octahedral coordinations and cation tetrahedral coordination in different directions). The position of layer-O and layer-T is alternate permutation. The crystal structure of pengzhizhongite (6 H ) may be expressed by …OT_2OT_1OT_1…, taaffeite (8 H ), …OT_2OT_1OT_2OT_1…, and nigerite (24 R ), … OT_1OT_2 OT_2OT_1 …×3 etc.. In their structure, there are not only the crystal structure units of spinel … OT_2 OT_2 … but also the units of nolanite … OT_1 OT_1 …. The research of these minerals has important theoretic and practical significance in the fields of minerals, gemology, material science etc..
文摘The domain structures in calcium-cerium fluorocarbonate mineral series from a rare earth mineral deposit within an aegirine alkali granite massif in Mianning County, Sichuan Province, China, were studied by means of transmission electron microscopy. Many categories of domain structures in this mineral series were observed and investigated, including the microtwin domains of parisite-6R(2) and B2S-6R, the antiphase domains of B2S-2H. The results show that the antiphase domains which are faults along crystal plane (0001) are formed by the displacement of crystal lattice in c * direction and the displacement is 0.471 nm. A new polytype (B4S2-3R) of regular mixed-layer structure with B4S2 type is found in the domain region of mixed-layer structure.
文摘In-situ formation fibrous polytype AlN composite ceramic materials was prepared from AlN-Y_2O_3-SiO_2 system.In comparison with AlN ceramics,both bending strength and fracture toughness of the composite materials are much bettered.Microstructural observation revealed that a lot of epitaxial growth fibrous AlN polytype occurred in matrix.Y_2O_3 seems to act as a densifier for in-situ formation materials and as medium for growth of fibrous polytype.SiO_2 is the growth promoter for fibrous polytype.The occurrnce of fibrous polytype may increase the strength and toughness of AlN ceramic composite mateirals.
基金financially supported by National Basic Research Program of China (No. 2011CB301904)the Natural Science Foundation of China (Nos. 11134006 and 61327808)
文摘The resistivities of vanadium-doped semi-insulating 4H-SiC wafers were measured by a contactless resistivity measurement system. Anomalous resistivity was found in semi-insulating 4H-SiC wafer. Raman spectra of semi-insulating4H-SiC wafer indicated that the anomalous resistivity was caused by polytype inclusion. Based on the activation energies of different SiC polytypes calculated from resistivity versus temperature data measured by COREMA-VT, the resistivities in the vanadium-doped semi-insulating 4H-SiC wafer with 6H polytype inclusion were calculated. The calculated resistivities are quite consistent with the measured resistivities. Furthermore, the compensation mechanism for the formation of anomalous resistivity was proposed.
文摘合成氟金云母多型种类与含量对云母的物理化学性质具有重要的影响。然而在X射线粉晶衍射(XRD)制样过程中云母00 l基面极易产生择优取向,严重制约了云母多型组成和含量的分析。传统撒样法可促使晶体取向随机分布,但制备的试样表面不够平坦。本文对传统撒样法进行改进,在撒样过程中使样品架均匀旋转,从而获得表面平坦的试样。XRD测试结果表明,旋转撒样法取向指数(OI=I 001/I 060)为3.9,与无择优取向的理论值4.5接近,明显优于正压法和侧装法(OI值分别为38.7和18.1),表明旋转撒样法能够显著减弱云母择优取向。这主要是由于旋转撒样法使晶体颗粒之间形成犬牙交错分布,提高了云母各晶面随机分布概率。Rietveld全图拟合分析显示,旋转撒样法获得的XRD数据精修效果较好,计算出本文合成的氟金云母样品中1 M和2 M 1多型含量分别为86%和14%,8个工业合成的氟金云母样品中1 M和2 M 1多型含量分别为57%~72%和28%~43%,并且存在较多的堆垛层错。总之,旋转撒样法减弱择优取向效果显著,为研究云母晶体生长、多型成因以及结构与性能之间的关系提供了技术支撑。
