Benefiting from the unique"Phonon-Glass,Electron-Crystal"(PGEC)characteristic,Zintl phases have been considered as a kind of promising thermoelectric materials.For the typical AM2X2 compounds with the CaAl2S...Benefiting from the unique"Phonon-Glass,Electron-Crystal"(PGEC)characteristic,Zintl phases have been considered as a kind of promising thermoelectric materials.For the typical AM2X2 compounds with the CaAl2Si2-type structure,YbMg_(2)Bi2 has shown competitive thermoelectric performance recently.Nevertheless,the optimization of YbMg_(2)Bi2 compounds is primarily focused on the substitution on Yb or Mg site.Herein,the Bi site is substituted by isoelectric Sb and the effect on the thermoelectric transport behavior is investigated.The partial substitution reduces the carrier concentration and induces the lattice deformation caused by the different atomic radius and mass between Bi and Sb,further leading to the decreased power factor and thermal conductivity.Fortunately,the reduction extent of the thermal conductivity outperforms that of power factor.Finally,the Sb substitution successfully results in a better thermoelectric performance compared with that of the pristine YbMg_(2)Bi1.98.Especially,the calculated energy conversion efficiency(a)of YbMg_(2)Bi1.88Sb0.1 which also possesses a relatively high output power density reaches the maximum value of 9.8% when Th=873 K,and Tc=300 K,respectively.This work demonstrates that the idea of substitution on anionic site should be a new strategy to achieve better ZT values for AM2X2 compounds.展开更多
Recently,Mg_(3)Sb_(2)-xBixalloys have attracted intensive attention,with the aim of maximizing the electrical transport performance via donor element doping,increasing the grain size,as well as electronic band structu...Recently,Mg_(3)Sb_(2)-xBixalloys have attracted intensive attention,with the aim of maximizing the electrical transport performance via donor element doping,increasing the grain size,as well as electronic band structure engineering.However,less attention has been paid to other significant factors,like how these intrinsic point defects and accompanied secondary phases influence thermoelectric properties.In this study,the microstructure and thermoelectric transport properties of Mg_(3.2)Sb_(0.5)Bi_(1.495-x)Te_(0.005)(x=0~0.2)compounds were systematically investigated,where tuning the Bi content shows the counter-intuitive impact on the thermoelectric properties.It was found that the Bipoor environment associated with Bi impurities facilitated the increment of cation vacancy formation energy and then increased the carrier concentration,leading to the enhancement of power factor.Simultaneously,the reduction of Bi-rich second phase content weakened the carrier scattering by grain boundaries whereas high carrier mobility was maintained.Moreover,the bipolar thermal conductivity decreased obviously due to the increased majority carrier concentration to suppress the intrinsic excitation.The synergistic optimization pushes the average ZT value(300-573 K)up to 0.95 in the Mg_(3.2)Sb_(0.5)Bi_(1.295)Te_(0.005)sample.Moreover,the calculated single-leg conversion efficiency is increased up to 9.7%with the hot-side temperature of 573 K,as the record-high value in this system.展开更多
Recently,n-type Mg3Sb1.5Bi0.5-based thermoelectric materials have attracted considerable attention for their extraordinary thermoelectric performance.Ideally,thermoelectric generators should be made of the same materi...Recently,n-type Mg3Sb1.5Bi0.5-based thermoelectric materials have attracted considerable attention for their extraordinary thermoelectric performance.Ideally,thermoelectric generators should be made of the same material system to avoid thermal mismatch in the practical application.In this work,p-type Mg3Sb1.5Bi0.5 which has almost the same composition as the state-of-the-art n-type Mg3.2Sb1.5Bi0.49-Te0.01Mn0.01 was synthesized by ball milling and spark plasma sintering,and then Na was chosen as an acceptor dopant to optimize the carrier concentration and further improve the thermoelectric performance.Na0.0075Mg2.9925Sb1.5Bi0.5 sample gets the highest ZT of~0.5 at 773 K.While Na0.005Mg2.995Sb1.5Bi0.5 sample shows the highest average ZT of~0.29 in the temperature range of 300 e773 K and matched thermal expansion behavior with the state-of-the-art n-type Mg3.2Sb1.5Bi0.49-Te0.01Mn0.01,which is of great significance for practical applications.Taking the Joule and Thompson heat into account,a high theoretical conversion efficiency(η)of~9.5%was calculated for the thermoelectric module consists of the present p-type Na0.005Mg2.995Sb1.5Bi0.5 and the state-of-the-art n-type Mg3.2Sb1.5Bi0.49Te0.01Mn0.01 with the leg length of 2 mm,and cold and hot side temperature of 300 K and 773 K,respectively,which shows a good potential for the use of this class of materials in the midtemperature power generation applications.展开更多
CaMg_(2)Bi_(2)-based compounds,a kind of the representative compounds of Zintl phases,have uniquely inherent layered structure and hence are considered to be potential thermoelectric materials.Generally,alloying is a ...CaMg_(2)Bi_(2)-based compounds,a kind of the representative compounds of Zintl phases,have uniquely inherent layered structure and hence are considered to be potential thermoelectric materials.Generally,alloying is a traditional and effective way to reduce the lattice thermal conductivity through the mass and strain field fluctuation between host and vip atoms.The cation sites have very few contributions to the band structure around the fermi level;thus,cation substitution may have negligible influence on the electric transport properties.What is more,widespread application of thermoelectric materials not only desires high ZT value but also calls for low-cost and environmentally benign constituent elements.Here,Ba substitution on cation site achieves a sharp reduction in lattice thermal conductivity through enhanced point defects scattering without the obvious sacrifice of high carrier mobility,and thus improves thermoelectric properties.Then,by combining further enhanced phonon scattering caused by isoelectronic substitution of Zn on the Mg site,an extraordinarily low lattice thermal conductivity of 0.51Wm^(-1) K^(-1) at 873 K is achieved in(Ca_(0.75)Ba_(0.25))_(0.995)Na_(0.005)Mg_(1.95)Zn_(0.05)Bi_(1.98) alloy,approaching the amorphous limit.Such maintenance of high mobility and realization of ultralow lattice thermal conductivity synergistically result in broadly improvement of the quality factorβ.Finally,a maximum ZT of 1.25 at 873K and the corresponding ZTave up to 0.85 from 300 K to 873K have been obtained for the same composition,meanwhile possessing temperature independent compatibility factor.To our knowledge,the current ZTave exceeds all the reported values in AMg_(2)Bi_(2)-based compounds so far.Furthermore,the low-cost and environmentfriendly characteristic plus excellent thermoelectric performance also make the present Zintl phase CaMg_(2)Bi_(2) more competitive in practical application.展开更多
Thermoelectric devices require thermoelectric materials with high figure-of-merit(ZT)values in the operating temperature range.In recent years,the Zintl phase compound,n-Mg_(3)Sb_(2),has received much attention owing ...Thermoelectric devices require thermoelectric materials with high figure-of-merit(ZT)values in the operating temperature range.In recent years,the Zintl phase compound,n-Mg_(3)Sb_(2),has received much attention owing to its rich chemistry and structural complexity.However,it hardly achieves high ZT values throughout the medium temperature range.Herein,by increasing the sintering temperature as much as possible,we successfully increased the average grain size of the compound by 15 times,and the grain boundary scattering was manipulated to obtain high carrier mobility of up to 180 cm^(2)V^(-1)s^(-1).Simultaneously,we optimized the Mg content for ultralow lattice thermal conductivity.We first doped the Mg_(3)Sb_(2)-based materials with boron for higher sintering temperature,good thermal stability,and higher hardness.The synergistic optimization of electrical and thermal transport resulted in excellent ZT values(0.62 at 300 K,1.81 at 773 K)and an average ZT of 1.4(from300 to 773 K),which are higher than the state-of-the-art values for n-type thermoelectric materials,demonstrating a high potential in device applications.展开更多
Environmentally friendly Mg_(3)Sb_(2)-based materials have drawn intensive attention owing to their promising thermoelectric performance.In this work,the electrical properties of p-type Mg_(3)Sb_(2) are dramatically o...Environmentally friendly Mg_(3)Sb_(2)-based materials have drawn intensive attention owing to their promising thermoelectric performance.In this work,the electrical properties of p-type Mg_(3)Sb_(2) are dramatically optimized by the regulation of Mg deficiency.Then,we,for the first time,found that Zn substitution at the Mg2 site leads to the alignment of px,y and pz orbital,resulting in a high band degeneracy and the dramatically enhanced Seebeck coefficient,demonstrated by the DFT calculations and electronic properties measurement.Moreover,Zn alloying decreases Mg1(Zn)vacancies formation energy and in turn increases Mg(Zn)vacancies and optimizes the carrier concentration.Simultaneously,the Mg/Zn substitutions,Mg vacancies,and porosity structure suppress the phonon transport in a broader frequency range,leading to a low lattice thermal conductivity of~0.47 W m^(-1) K^(-1) at 773 K.Finally,a high ZT of~0.87 at 773 K was obtained for Mg_(1.95)Na_(0.01)Zn_(1)Sb_(2),exceeding most of the previously reported p-type Mg_(3)Sb_(2) compounds.Our results further demonstrate the promising prospects of p-type Mg_(3)Sb_(2)-based material in the field of mid-temperature heat recovery.展开更多
基金supported financially by the National Natural Science Foundation of China(Nos.51771065 and 51871082)。
文摘Benefiting from the unique"Phonon-Glass,Electron-Crystal"(PGEC)characteristic,Zintl phases have been considered as a kind of promising thermoelectric materials.For the typical AM2X2 compounds with the CaAl2Si2-type structure,YbMg_(2)Bi2 has shown competitive thermoelectric performance recently.Nevertheless,the optimization of YbMg_(2)Bi2 compounds is primarily focused on the substitution on Yb or Mg site.Herein,the Bi site is substituted by isoelectric Sb and the effect on the thermoelectric transport behavior is investigated.The partial substitution reduces the carrier concentration and induces the lattice deformation caused by the different atomic radius and mass between Bi and Sb,further leading to the decreased power factor and thermal conductivity.Fortunately,the reduction extent of the thermal conductivity outperforms that of power factor.Finally,the Sb substitution successfully results in a better thermoelectric performance compared with that of the pristine YbMg_(2)Bi1.98.Especially,the calculated energy conversion efficiency(a)of YbMg_(2)Bi1.88Sb0.1 which also possesses a relatively high output power density reaches the maximum value of 9.8% when Th=873 K,and Tc=300 K,respectively.This work demonstrates that the idea of substitution on anionic site should be a new strategy to achieve better ZT values for AM2X2 compounds.
基金National Natural Science Foundation of China(Nos.52130106)Heilongjiang Touyan Innovation Team ProgramFundamental Research Funds for the Central Universities(FRFCU5710053021 and HIT.OCEF.2021014)。
文摘Recently,Mg_(3)Sb_(2)-xBixalloys have attracted intensive attention,with the aim of maximizing the electrical transport performance via donor element doping,increasing the grain size,as well as electronic band structure engineering.However,less attention has been paid to other significant factors,like how these intrinsic point defects and accompanied secondary phases influence thermoelectric properties.In this study,the microstructure and thermoelectric transport properties of Mg_(3.2)Sb_(0.5)Bi_(1.495-x)Te_(0.005)(x=0~0.2)compounds were systematically investigated,where tuning the Bi content shows the counter-intuitive impact on the thermoelectric properties.It was found that the Bipoor environment associated with Bi impurities facilitated the increment of cation vacancy formation energy and then increased the carrier concentration,leading to the enhancement of power factor.Simultaneously,the reduction of Bi-rich second phase content weakened the carrier scattering by grain boundaries whereas high carrier mobility was maintained.Moreover,the bipolar thermal conductivity decreased obviously due to the increased majority carrier concentration to suppress the intrinsic excitation.The synergistic optimization pushes the average ZT value(300-573 K)up to 0.95 in the Mg_(3.2)Sb_(0.5)Bi_(1.295)Te_(0.005)sample.Moreover,the calculated single-leg conversion efficiency is increased up to 9.7%with the hot-side temperature of 573 K,as the record-high value in this system.
基金the National Natural Science Foundation of China(Nos.51771065 and 51871082).
文摘Recently,n-type Mg3Sb1.5Bi0.5-based thermoelectric materials have attracted considerable attention for their extraordinary thermoelectric performance.Ideally,thermoelectric generators should be made of the same material system to avoid thermal mismatch in the practical application.In this work,p-type Mg3Sb1.5Bi0.5 which has almost the same composition as the state-of-the-art n-type Mg3.2Sb1.5Bi0.49-Te0.01Mn0.01 was synthesized by ball milling and spark plasma sintering,and then Na was chosen as an acceptor dopant to optimize the carrier concentration and further improve the thermoelectric performance.Na0.0075Mg2.9925Sb1.5Bi0.5 sample gets the highest ZT of~0.5 at 773 K.While Na0.005Mg2.995Sb1.5Bi0.5 sample shows the highest average ZT of~0.29 in the temperature range of 300 e773 K and matched thermal expansion behavior with the state-of-the-art n-type Mg3.2Sb1.5Bi0.49-Te0.01Mn0.01,which is of great significance for practical applications.Taking the Joule and Thompson heat into account,a high theoretical conversion efficiency(η)of~9.5%was calculated for the thermoelectric module consists of the present p-type Na0.005Mg2.995Sb1.5Bi0.5 and the state-of-the-art n-type Mg3.2Sb1.5Bi0.49Te0.01Mn0.01 with the leg length of 2 mm,and cold and hot side temperature of 300 K and 773 K,respectively,which shows a good potential for the use of this class of materials in the midtemperature power generation applications.
基金This work was supported by the National Natural Science Foundation of China(Nos.51771065 and 51871082).
文摘CaMg_(2)Bi_(2)-based compounds,a kind of the representative compounds of Zintl phases,have uniquely inherent layered structure and hence are considered to be potential thermoelectric materials.Generally,alloying is a traditional and effective way to reduce the lattice thermal conductivity through the mass and strain field fluctuation between host and vip atoms.The cation sites have very few contributions to the band structure around the fermi level;thus,cation substitution may have negligible influence on the electric transport properties.What is more,widespread application of thermoelectric materials not only desires high ZT value but also calls for low-cost and environmentally benign constituent elements.Here,Ba substitution on cation site achieves a sharp reduction in lattice thermal conductivity through enhanced point defects scattering without the obvious sacrifice of high carrier mobility,and thus improves thermoelectric properties.Then,by combining further enhanced phonon scattering caused by isoelectronic substitution of Zn on the Mg site,an extraordinarily low lattice thermal conductivity of 0.51Wm^(-1) K^(-1) at 873 K is achieved in(Ca_(0.75)Ba_(0.25))_(0.995)Na_(0.005)Mg_(1.95)Zn_(0.05)Bi_(1.98) alloy,approaching the amorphous limit.Such maintenance of high mobility and realization of ultralow lattice thermal conductivity synergistically result in broadly improvement of the quality factorβ.Finally,a maximum ZT of 1.25 at 873K and the corresponding ZTave up to 0.85 from 300 K to 873K have been obtained for the same composition,meanwhile possessing temperature independent compatibility factor.To our knowledge,the current ZTave exceeds all the reported values in AMg_(2)Bi_(2)-based compounds so far.Furthermore,the low-cost and environmentfriendly characteristic plus excellent thermoelectric performance also make the present Zintl phase CaMg_(2)Bi_(2) more competitive in practical application.
基金supported by the National Natural Science Foundation of China(51771065 and 51871082)the Natural Science Foundation of Heilongjiang Province of China(ZD2020E003)。
文摘Thermoelectric devices require thermoelectric materials with high figure-of-merit(ZT)values in the operating temperature range.In recent years,the Zintl phase compound,n-Mg_(3)Sb_(2),has received much attention owing to its rich chemistry and structural complexity.However,it hardly achieves high ZT values throughout the medium temperature range.Herein,by increasing the sintering temperature as much as possible,we successfully increased the average grain size of the compound by 15 times,and the grain boundary scattering was manipulated to obtain high carrier mobility of up to 180 cm^(2)V^(-1)s^(-1).Simultaneously,we optimized the Mg content for ultralow lattice thermal conductivity.We first doped the Mg_(3)Sb_(2)-based materials with boron for higher sintering temperature,good thermal stability,and higher hardness.The synergistic optimization of electrical and thermal transport resulted in excellent ZT values(0.62 at 300 K,1.81 at 773 K)and an average ZT of 1.4(from300 to 773 K),which are higher than the state-of-the-art values for n-type thermoelectric materials,demonstrating a high potential in device applications.
基金This work was funded by the National Natural Science Foundation of China(Nos.52130106,51871082,and 52101247)the Natural Science Foundation of Heilongjiang Province of China(No.ZD 2020E003)the Heilongjiang Touyan Innovation Team Program.Thanks to the support from the Fundamental Research Funds for the Central Universities(FRFCU5710053021 and HIT.OCEF.2021014).
文摘Environmentally friendly Mg_(3)Sb_(2)-based materials have drawn intensive attention owing to their promising thermoelectric performance.In this work,the electrical properties of p-type Mg_(3)Sb_(2) are dramatically optimized by the regulation of Mg deficiency.Then,we,for the first time,found that Zn substitution at the Mg2 site leads to the alignment of px,y and pz orbital,resulting in a high band degeneracy and the dramatically enhanced Seebeck coefficient,demonstrated by the DFT calculations and electronic properties measurement.Moreover,Zn alloying decreases Mg1(Zn)vacancies formation energy and in turn increases Mg(Zn)vacancies and optimizes the carrier concentration.Simultaneously,the Mg/Zn substitutions,Mg vacancies,and porosity structure suppress the phonon transport in a broader frequency range,leading to a low lattice thermal conductivity of~0.47 W m^(-1) K^(-1) at 773 K.Finally,a high ZT of~0.87 at 773 K was obtained for Mg_(1.95)Na_(0.01)Zn_(1)Sb_(2),exceeding most of the previously reported p-type Mg_(3)Sb_(2) compounds.Our results further demonstrate the promising prospects of p-type Mg_(3)Sb_(2)-based material in the field of mid-temperature heat recovery.
