Boundary engineering has proven effective in enhancing the thermoelectric performance of materials.SnSe,known for its low thermal conductivity,has garnered significant interest;however,its application is hindered by p...Boundary engineering has proven effective in enhancing the thermoelectric performance of materials.SnSe,known for its low thermal conductivity,has garnered significant interest;however,its application is hindered by poor electrical conductivity.Herein,the Ag_(8)GeSe_(6) is introduced into the p-type polycrystalline SnSe matrix to optimize the thermoelectric performance,and the in-situ Ag_(2)Se precipitates are formed in grain boundaries,which play dual roles,acting as an electron attraction center for improving hole concentration and a phonon scattering center for reducing lattice thermal conductivity.It effectively decouples the thermal and electrical transport properties to optimize the thermoelectric performance.Importantly,the amount of Ag_(2)Se can be controlled by adjusting the amount of Ag_(8)GeSe_(6) added to the SnSe matrix.The introduction of Ag_(8)GeSe_(6) enhances electrical conductivity due to the increased hole carrier caused by the introduced Ag+and the formed electron attraction center(in-situ Ag_(2)Se precipitates).Based on the DFT calculations,the band gap of the Ag_(8)GeSe_(6)-doped samples is considerably decreased,facilitating carrier transport.As a result,the electrical transport properties increase to 808μW m^(−1) K^(−2) at 823 K for SnSe+0.5 wt%Ag_(8)GeSe_(6).In addition,in-situ Ag_(2)Se precipitates in grain boundaries strongly enhance phonon scattering,causing a decrease in lattice thermal conductivity.Furthermore,the presence of defects contributes to a reduction in lattice thermal conductivity.Specifically,the thermal conductivity of SnSe+1.0 wt%Ag_(8)GeSe_(6) decreases to 0.29 W m^(−1) K^(−1) at 823 K.Consequently,SnSe+0.5 wt%Ag_(8)GeSe_(6) obtains a high ZT value of 1.7 at 823 K and maintains a high average ZT value of 0.57 over the temperature range of 323−773 K.Additionally,the mechanical properties of Ag_(8)GeSe_(6)-doped also show an improvement.These advancements can be applied to energy supply applications during deep space exploration.展开更多
This study presents findings of indoor environmental quality （IEQ） investigations conducted in elementary schools＇ classrooms in the United Arab Emirates （UAE）. Average TVOC, CO2, O3, CO, and particle concentrati...This study presents findings of indoor environmental quality （IEQ） investigations conducted in elementary schools＇ classrooms in the United Arab Emirates （UAE）. Average TVOC, CO2, O3, CO, and particle concentrations measured in the classrooms were 815 pg / m^3, 1605 ppm, 0.05 ppm, 1.16 ppm, and 1730 μg/m^3, respectively. Whereas, local authority known as Dubai Municipality recommended 300 pg/m^3, 800 ppm, 0.06 ppm, 9 ppm, and 150-300 μg/m^3 for TVOC, CO2, O3, CO, and particle, respectively. Dubai Municipality recommended temperature and retative humidity （RH） levels of 22.5 ℃ to 25.5 ℃ and 30%-60%, respectively. Average temperature and RH levels measured in the classrooms were 24.5 ℃ and 40.4%, respectively. Average sound level in the classrooms was 24 dB greater than recommended sound level limit of 35 dB. Six （6） classrooms had average lux levels in the range of 400-800 lux. Two （2） classrooms had average lux levels in the range of 100 200 lux. The remaining classrooms had lux levels around the recommended 300 lux. High occupancy density was observed in majority of the studied classrooms. Observations during walkthroush investigations could展开更多
基金supported by the Outstanding Youth Fund of Yunnan Province(Grant No.202201AV070005)the National Natural Science Foundation of China(Grant No.52162029)the National Key R&D Program of China(Grant No.2022YFF0503804).
文摘Boundary engineering has proven effective in enhancing the thermoelectric performance of materials.SnSe,known for its low thermal conductivity,has garnered significant interest;however,its application is hindered by poor electrical conductivity.Herein,the Ag_(8)GeSe_(6) is introduced into the p-type polycrystalline SnSe matrix to optimize the thermoelectric performance,and the in-situ Ag_(2)Se precipitates are formed in grain boundaries,which play dual roles,acting as an electron attraction center for improving hole concentration and a phonon scattering center for reducing lattice thermal conductivity.It effectively decouples the thermal and electrical transport properties to optimize the thermoelectric performance.Importantly,the amount of Ag_(2)Se can be controlled by adjusting the amount of Ag_(8)GeSe_(6) added to the SnSe matrix.The introduction of Ag_(8)GeSe_(6) enhances electrical conductivity due to the increased hole carrier caused by the introduced Ag+and the formed electron attraction center(in-situ Ag_(2)Se precipitates).Based on the DFT calculations,the band gap of the Ag_(8)GeSe_(6)-doped samples is considerably decreased,facilitating carrier transport.As a result,the electrical transport properties increase to 808μW m^(−1) K^(−2) at 823 K for SnSe+0.5 wt%Ag_(8)GeSe_(6).In addition,in-situ Ag_(2)Se precipitates in grain boundaries strongly enhance phonon scattering,causing a decrease in lattice thermal conductivity.Furthermore,the presence of defects contributes to a reduction in lattice thermal conductivity.Specifically,the thermal conductivity of SnSe+1.0 wt%Ag_(8)GeSe_(6) decreases to 0.29 W m^(−1) K^(−1) at 823 K.Consequently,SnSe+0.5 wt%Ag_(8)GeSe_(6) obtains a high ZT value of 1.7 at 823 K and maintains a high average ZT value of 0.57 over the temperature range of 323−773 K.Additionally,the mechanical properties of Ag_(8)GeSe_(6)-doped also show an improvement.These advancements can be applied to energy supply applications during deep space exploration.
文摘This study presents findings of indoor environmental quality （IEQ） investigations conducted in elementary schools＇ classrooms in the United Arab Emirates （UAE）. Average TVOC, CO2, O3, CO, and particle concentrations measured in the classrooms were 815 pg / m^3, 1605 ppm, 0.05 ppm, 1.16 ppm, and 1730 μg/m^3, respectively. Whereas, local authority known as Dubai Municipality recommended 300 pg/m^3, 800 ppm, 0.06 ppm, 9 ppm, and 150-300 μg/m^3 for TVOC, CO2, O3, CO, and particle, respectively. Dubai Municipality recommended temperature and retative humidity （RH） levels of 22.5 ℃ to 25.5 ℃ and 30%-60%, respectively. Average temperature and RH levels measured in the classrooms were 24.5 ℃ and 40.4%, respectively. Average sound level in the classrooms was 24 dB greater than recommended sound level limit of 35 dB. Six （6） classrooms had average lux levels in the range of 400-800 lux. Two （2） classrooms had average lux levels in the range of 100 200 lux. The remaining classrooms had lux levels around the recommended 300 lux. High occupancy density was observed in majority of the studied classrooms. Observations during walkthroush investigations could
