The colourless IaA-type gem-quality diamond crystals containing a high concentration of nitrogen(1500–1700 ppm)were successfully prepared by annealing the as-grown Ib-type N-doped diamonds at a high temperature and h...The colourless IaA-type gem-quality diamond crystals containing a high concentration of nitrogen(1500–1700 ppm)were successfully prepared by annealing the as-grown Ib-type N-doped diamonds at a high temperature and high pressure in China-type cubic anvil high-pressure apparatus.Experiments were carried out at pressures of 6.5–7.0 GPa and temperatures from 1900 K to 2100 K.Annealing treatment on high-level N-doped diamond crystals shows that the colour of the diamond crystals is obviously reduced from green to colourless after annealing treatment within 1 h at a higher temperature,which is induced by nitrogen aggregation in the diamond lattice indicated by infrared(IR)spectroscopy.It is further revealed that active energy of the nitrogen atom transforming from the dispersed form to the aggregated form is much lower than that in the standard Ib-type diamond crystals with nitrogen concentration less than 300 ppm.The colourless IaA-type diamond crystal prepared by annealing at 2100 K displays the same properties in IR spectra as the high-quality natural diamonds which are classified into the IaA type.展开更多
CrO_(2)-TiO_(2) composites are synthesized by using a high temperature and high pressure method using CrO_(3) and H_(2)TiO_(3) as precursors.The composites consist of large rod-like CrO_(2) crystals separated by small...CrO_(2)-TiO_(2) composites are synthesized by using a high temperature and high pressure method using CrO_(3) and H_(2)TiO_(3) as precursors.The composites consist of large rod-like CrO_(2) crystals separated by small TiO_(2) grains.The CrO_(2) in the composites is very pure and its saturation magnetization is very close to the theoretical value(i.e.,2μ_(B) per formula unit).The composites exhibit a large negative magnetoresistance(MR)at 5 K.The MR in CrO_(2)-TiO_(2) composites is mainly attributed to spin-polarized tunneling between CrO_(2) crystals.The conductivity of the composites is best described by a fluctuation-induced tunneling model below 230 K.展开更多
Determining the best set of beveling parameters is an advantageous characteristic of the geometrical conditions for a cubic high-pressure tungsten carbide(WC)anvil,but it is almost impossible to deduce experimentally(...Determining the best set of beveling parameters is an advantageous characteristic of the geometrical conditions for a cubic high-pressure tungsten carbide(WC)anvil,but it is almost impossible to deduce experimentally(much affected by defects in the material).In order to remove the affection of defects in materials,we investigate computational stress analyses in different beveling parameters of WC anvils by the finite element method.The results indicate that the rate of cell pressure transmitting and failure crack in the WC anvil monotonically increases with the bevel angle from 42°to 45°.Furthermore,there are two groups of actual users of beveled anvils,one group preferring 41.5°,which can decrease the rate of failure crack in WC anvil,the other group preferring 42°,which can increase the rate of cell pressure transmitting.This work would give an effective solution to solve the problem of the design of a cubic high-pressure WC anvil experimentally and will greatly help to improve the cubic high-pressure WC anvil type high pressure techniques.展开更多
It is significant to investigate the action of nitrogen getters,which are used to synthesize type-IIa large diamond single crystals under high pressure and high temperature(HPHT).The reaction mechanism of Al as a nitr...It is significant to investigate the action of nitrogen getters,which are used to synthesize type-IIa large diamond single crystals under high pressure and high temperature(HPHT).The reaction mechanism of Al as a nitrogen getter and N in the HPHT alloy solvent is still indeterminate at present.In order to investigate the reaction of Al and N in the HPHT alloy solvent,Al and AlN are respectively added to the system of Fe55Ni29Co16−C(wt%,abbr.FeNiCo-C)for the synthesis of diamonds at about 5.5 GPa and 1600 K.The concentration of nitrogen in the diamonds is characterized by a micro Fourier transform infrared(micro-FTIR)spectrometer.The experimental results show that cN decreases when Al is added to the FeNiCo-C system.However,it increases when AlN is added.A reversible reaction confirms that Al and N can react and form AlN,simultaneously AlN can be decomposed into Al and N in the HPHT alloy solvent.Therefore the mechanism of eliminating the nitrogen of nitrogen getter Al is realized in detail.展开更多
Polycrystalline skutterudites Ba_(0.32)Co_(4)Sb_(12-x)Tex(nominally x=0.1-0.7)are synthesized by the high pressure and high temperature(HPHT)method.The influence of Te substitution on electrical transport properties a...Polycrystalline skutterudites Ba_(0.32)Co_(4)Sb_(12-x)Tex(nominally x=0.1-0.7)are synthesized by the high pressure and high temperature(HPHT)method.The influence of Te substitution on electrical transport properties are investigated in the temperature range of 300-710K.All the samples show n-type conduction.It is found that the presence of Te substantially decreases electrical resistivi by without any detrimental effect on the Seebeck coefficients,which improves the power factor.Among all the samples,Ba_(0.32)Co_(4)Sb_(11.5)Te_(0.5)shows the highest thermoelectric figure of merit of 0.76 at 710K.展开更多
A thermoelectric material Smx Co4Sb12 （0（ x ≤1.0） is synthesized at high pressure and high temperature leading to an enhanced power factor. The experimental measurements show that the SmxCo4Sb12 compounds exhibits...A thermoelectric material Smx Co4Sb12 （0（ x ≤1.0） is synthesized at high pressure and high temperature leading to an enhanced power factor. The experimental measurements show that the SmxCo4Sb12 compounds exhibits n-type conduction. The absolute value of the Seebeck coefficient decreases with increasing Sm fraction. The resistivity increases with samarium content x from 0.1 to 0.2, but decreases dramatically when x changes from 0.2 to 1.0. The maximum power factor reaches 13.1 μW.cm^-1K-2 at x =1.0, which is larger than the data previously reported for the La-doped CoSb3 prepared at room pressure.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 51172089.
文摘The colourless IaA-type gem-quality diamond crystals containing a high concentration of nitrogen(1500–1700 ppm)were successfully prepared by annealing the as-grown Ib-type N-doped diamonds at a high temperature and high pressure in China-type cubic anvil high-pressure apparatus.Experiments were carried out at pressures of 6.5–7.0 GPa and temperatures from 1900 K to 2100 K.Annealing treatment on high-level N-doped diamond crystals shows that the colour of the diamond crystals is obviously reduced from green to colourless after annealing treatment within 1 h at a higher temperature,which is induced by nitrogen aggregation in the diamond lattice indicated by infrared(IR)spectroscopy.It is further revealed that active energy of the nitrogen atom transforming from the dispersed form to the aggregated form is much lower than that in the standard Ib-type diamond crystals with nitrogen concentration less than 300 ppm.The colourless IaA-type diamond crystal prepared by annealing at 2100 K displays the same properties in IR spectra as the high-quality natural diamonds which are classified into the IaA type.
基金Supported by the National Natural Science Foundation of China under Grant No 50972048the Program for New Century Excellent Talents in University.
文摘CrO_(2)-TiO_(2) composites are synthesized by using a high temperature and high pressure method using CrO_(3) and H_(2)TiO_(3) as precursors.The composites consist of large rod-like CrO_(2) crystals separated by small TiO_(2) grains.The CrO_(2) in the composites is very pure and its saturation magnetization is very close to the theoretical value(i.e.,2μ_(B) per formula unit).The composites exhibit a large negative magnetoresistance(MR)at 5 K.The MR in CrO_(2)-TiO_(2) composites is mainly attributed to spin-polarized tunneling between CrO_(2) crystals.The conductivity of the composites is best described by a fluctuation-induced tunneling model below 230 K.
基金Supported by the National Natural Science Foundation of China under Grant No 11204102the China Postdoctoral Science Foundation under Grant No 2011M500592+1 种基金Shanghai Key Laboratory of Digitized Auto-Body under Grant No 2010001Jilin University Science Foundation.
文摘Determining the best set of beveling parameters is an advantageous characteristic of the geometrical conditions for a cubic high-pressure tungsten carbide(WC)anvil,but it is almost impossible to deduce experimentally(much affected by defects in the material).In order to remove the affection of defects in materials,we investigate computational stress analyses in different beveling parameters of WC anvils by the finite element method.The results indicate that the rate of cell pressure transmitting and failure crack in the WC anvil monotonically increases with the bevel angle from 42°to 45°.Furthermore,there are two groups of actual users of beveled anvils,one group preferring 41.5°,which can decrease the rate of failure crack in WC anvil,the other group preferring 42°,which can increase the rate of cell pressure transmitting.This work would give an effective solution to solve the problem of the design of a cubic high-pressure WC anvil experimentally and will greatly help to improve the cubic high-pressure WC anvil type high pressure techniques.
基金by the National Natural Science Foundation of China under Grant No 50572032the Doctor Foundation of Henan Polytechnic University(648438).
文摘It is significant to investigate the action of nitrogen getters,which are used to synthesize type-IIa large diamond single crystals under high pressure and high temperature(HPHT).The reaction mechanism of Al as a nitrogen getter and N in the HPHT alloy solvent is still indeterminate at present.In order to investigate the reaction of Al and N in the HPHT alloy solvent,Al and AlN are respectively added to the system of Fe55Ni29Co16−C(wt%,abbr.FeNiCo-C)for the synthesis of diamonds at about 5.5 GPa and 1600 K.The concentration of nitrogen in the diamonds is characterized by a micro Fourier transform infrared(micro-FTIR)spectrometer.The experimental results show that cN decreases when Al is added to the FeNiCo-C system.However,it increases when AlN is added.A reversible reaction confirms that Al and N can react and form AlN,simultaneously AlN can be decomposed into Al and N in the HPHT alloy solvent.Therefore the mechanism of eliminating the nitrogen of nitrogen getter Al is realized in detail.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50731006 and 50801030.
文摘Polycrystalline skutterudites Ba_(0.32)Co_(4)Sb_(12-x)Tex(nominally x=0.1-0.7)are synthesized by the high pressure and high temperature(HPHT)method.The influence of Te substitution on electrical transport properties are investigated in the temperature range of 300-710K.All the samples show n-type conduction.It is found that the presence of Te substantially decreases electrical resistivi by without any detrimental effect on the Seebeck coefficients,which improves the power factor.Among all the samples,Ba_(0.32)Co_(4)Sb_(11.5)Te_(0.5)shows the highest thermoelectric figure of merit of 0.76 at 710K.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50731006 and 50801030.
文摘A thermoelectric material Smx Co4Sb12 （0（ x ≤1.0） is synthesized at high pressure and high temperature leading to an enhanced power factor. The experimental measurements show that the SmxCo4Sb12 compounds exhibits n-type conduction. The absolute value of the Seebeck coefficient decreases with increasing Sm fraction. The resistivity increases with samarium content x from 0.1 to 0.2, but decreases dramatically when x changes from 0.2 to 1.0. The maximum power factor reaches 13.1 μW.cm^-1K-2 at x =1.0, which is larger than the data previously reported for the La-doped CoSb3 prepared at room pressure.
