Ga摻雜對(duì)Cu3SbSe4熱電性能的影響?

陳蘿娜 劉葉烽 張繼業(yè) 楊炯 邢娟娟 駱軍 張文清

(上海大學(xué)材料科學(xué)與工程學(xué)院,上海 200444)

Ga摻雜對(duì)Cu3SbSe4熱電性能的影響?

陳蘿娜 劉葉烽 張繼業(yè) 楊炯 邢娟娟 駱軍?張文清?

(上海大學(xué)材料科學(xué)與工程學(xué)院,上海 200444)

(2017年4月20日收到;2017年6月9日收到修改稿)

采用熔融-淬火方法制備了Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)樣品,系統(tǒng)地研究了Ga在Sb位摻雜對(duì)Cu3SbSe4熱電性能的影響.研究結(jié)果表明,少量的Ga摻雜(x=0.01)可以有效提高空穴濃度,抑制本征激發(fā),改善樣品的電輸運(yùn)性能.摻Ga樣品在625 K時(shí)功率因子達(dá)到最大值10μW/cm.K2,比未摻Ga的Cu2.95SbSe4樣品提高了約一倍.但是隨著Ga摻雜濃度的進(jìn)一步提高,缺陷對(duì)載流子的散射增強(qiáng),同時(shí)載流子有效質(zhì)量增大,導(dǎo)致載流子遷移率急劇下降.因此Ga含量增加反而使樣品的電性能惡化.在熱輸運(yùn)方面,Ga摻雜可以有效降低雙極擴(kuò)散對(duì)熱導(dǎo)率的貢獻(xiàn),同時(shí)摻雜引入的點(diǎn)缺陷對(duì)高頻聲子有較強(qiáng)的散射作用,因此高溫區(qū)的熱導(dǎo)率明顯降低.最終該體系在664 K時(shí)獲得最大ZT值0.53,比未摻Ga的樣品提高了近50%.

Ga摻雜,Cu3SbSe4,熱電性能

1 引 言

熱電材料是一種通過固體內(nèi)部載流子運(yùn)動(dòng)實(shí)現(xiàn)電-熱相互轉(zhuǎn)換的清潔能源材料.利用熱電材料的Seebeck效應(yīng)和Peltier效應(yīng),可以分別實(shí)現(xiàn)熱電裝置的發(fā)電和制冷功能.與傳統(tǒng)的發(fā)電和制冷裝置相比,熱電裝置具有體積小、質(zhì)量輕、無污染、無噪音、使用壽命長(zhǎng)等優(yōu)點(diǎn)[1?3].通常,材料的熱電性能采用無量綱熱電優(yōu)值ZT來衡量,

式中σ、S和κ分別為電導(dǎo)率、Seebeck系數(shù)和熱導(dǎo)率.但是,以上三個(gè)參數(shù)并不是相互獨(dú)立的,它們都與材料的電子結(jié)構(gòu)和載流子輸運(yùn)特性相關(guān),因此ZT值的提高需要協(xié)同調(diào)控這些相互關(guān)聯(lián)的參數(shù)[4].目前調(diào)控?zé)犭娦阅艿姆椒ㄖ饕袃煞N:一是通過能帶工程[5],或者引入共振能級(jí)[6,7]、量子限域效應(yīng)[8]以及能量過濾效應(yīng)等[9]來增大材料的Seebeck系數(shù),提高其功率因子PF(σS2);二是通過引入不同尺度的晶體缺陷來增強(qiáng)聲子散射(包括納米析出相、晶界、位錯(cuò)、點(diǎn)缺陷等),降低材料的晶格熱導(dǎo)率(κlattice)[10,11].

近年來,類金剛石結(jié)構(gòu)的Cu基三元化合物(如Cu2GeSe3,Cu2SnSe3,CuGaTe2,Cu InTe2,Cu2ZnGeSe4和Cu3SbS4等),因具有較好的熱電性能受到了廣泛的關(guān)注[12?18].其中,Cu3SbSe4是一種帶隙較小(0.29 eV)的p型半導(dǎo)體材料[19],該材料在650 K左右時(shí)ZT值達(dá)到最大(約為0.25).相對(duì)于性能優(yōu)異的傳統(tǒng)中溫區(qū)熱電材料PbTe[20]而言,Cu3SbSe4具有無有害元素且成本較低的優(yōu)點(diǎn).但是未摻雜的Cu3SbSe4化合物由于載流子濃度低,電導(dǎo)率較小,因而對(duì)其熱電性能的優(yōu)化主要集中于通過摻雜提高其載流子濃度.Do和Mahanti[21]基于第一性原理計(jì)算,對(duì)Cu3SbSe4各個(gè)位置的雜質(zhì)形成能進(jìn)行了研究.結(jié)果表明,這種材料易形成含Cu空位的p型半導(dǎo)體,同時(shí)其Sb位的雜質(zhì)形成能較低,是最容易摻雜的位置.目前的實(shí)驗(yàn)研究與上述理論計(jì)算結(jié)果一致,較為有效的摻雜大部分是在Sb位進(jìn)行的受主摻雜.

Yang等[22]發(fā)現(xiàn)通過在Sb位摻雜Sn可以有效提高Cu3SbSe4的電導(dǎo)率,其ZT值在673 K時(shí)可達(dá)約0.75,相比未摻雜的Cu3SbSe4提高了2倍.Wei等[19]發(fā)現(xiàn)Cu3SbSe4價(jià)帶頂并非之前理論計(jì)算所預(yù)測(cè)的三重簡(jiǎn)并態(tài),因此通過摻雜提高體系的空穴濃度會(huì)同步提高空穴的有效質(zhì)量,為該體系電輸運(yùn)性能的優(yōu)化提供了指導(dǎo).Qin等[23]對(duì)Sb位摻雜Bi進(jìn)行了研究,體系的ZT值在600 K時(shí)達(dá)到了0.7左右.Li等[24]進(jìn)一步對(duì)Sn摻雜Cu3SbSe4的微結(jié)構(gòu)進(jìn)行了優(yōu)化,把ZT值提高到1.05左右.最近,Liu等[25]通過在Cu3SbSe4的Sb位進(jìn)行Sn和Bi共摻雜,在673 K時(shí)獲得了高達(dá)1.26的熱電優(yōu)值,是目前報(bào)道的p型Cu3SbSe4材料的最高ZT值.此外,Li等[26]和Zhang等[27]分別在Sb位摻雜了第三主族元素A l和In,獲得的最大ZT值分別為0.58和0.5.

在本文的工作中,我們考慮到Ga3+和Sb5+離子半徑相近(都約為0.62?),因此Ga3+可能較容易取代Sb5+,從而有效提高Cu3SbSe4的空穴濃度和電導(dǎo)率(缺陷反應(yīng)如(2)式).另外,Wei等[19,28]指出,在Cu3SbSe4中引入適當(dāng)?shù)腃u空位有助于補(bǔ)償高溫?zé)Y(jié)過程中Se元素的揮發(fā),同時(shí)Cu空位的引入也可以進(jìn)一步增加樣品的空穴濃度(缺陷反應(yīng)如(3)式),從而獲得更好的熱電性能.因此,本文采用熔融-淬火方法制備了Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)樣品,并系統(tǒng)研究了Ga替代Sb對(duì)Cu3SbSe4電、熱輸運(yùn)性能的影響.

2 實(shí)驗(yàn)方法

2.1 樣品制備

在Ar氣氛的保護(hù)下,按照化學(xué)計(jì)量比Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 和0.04)配制Cu粉(99.9%),Sb粒(99.99%),Se粉(99.99%)和Ga塊(99.9999%),并置于石墨坩堝中,隨后將石墨坩堝真空密封于石英管中.然后將石英管放入立式管式爐中,緩慢升溫到1173 K(升溫時(shí)間30 h),并在此溫度下保溫10 h,隨后緩慢降溫到773 K,并退火5 d以保證樣品的均勻性,最后淬火得到塊狀樣品.利用研缽將樣品磨成粉后,在400?C和45 MPa壓力下熱壓燒結(jié)成圓片狀樣品,進(jìn)一步切割成合適的形狀后用于后續(xù)的熱電性能測(cè)試.

2.2 樣品表征

利用粉末X射線衍射(XRD)進(jìn)行物相分析,設(shè)備為日本理學(xué)公司D/max-2200X(Cu Kα)衍射儀.利用ULVAC-RIKO ZEM-3測(cè)試樣品的電導(dǎo)率(σ)和Seebeck系數(shù)(S).樣品的熱擴(kuò)散系數(shù)(α)利用Netzsch LFA 457(cowan+脈沖修正)激光熱導(dǎo)儀測(cè)試,比熱(CP)利用差示掃描量熱法(DSC,Netzsch DSC214)進(jìn)行表征.樣品的密度(D)由阿基米德排水法測(cè)量.樣品的總熱導(dǎo)率(κtot)根據(jù)公式κtot=D×CP×α計(jì)算得到.利用場(chǎng)發(fā)射掃描電子顯微鏡(SEM,Zeiss GeMini300,Germany)進(jìn)行微結(jié)構(gòu)表征.樣品的實(shí)際成分由能量色散X射線譜(energy-dispersive X-ray spectroscopy,EDXS)確定.

3 實(shí)驗(yàn)結(jié)果與討論

圖1 (網(wǎng)刊彩色)樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)的(a)XRD圖譜以及(b)(112)衍射峰和(c)(332)衍射峰的放大圖Fig.1. (color on line)(a)XRD patterns for Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)samp les and Magnified peaks for(b)(112)and(c)(332)d iff raction.

圖1為樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02,0.04)的室溫XRD圖譜.XRD分析結(jié)果表明所有樣品的晶體結(jié)構(gòu)均為四方相的脆硫銻銅礦結(jié)構(gòu)(PDF#085-0003),空間群為I2m. 隨著Ga摻雜量的增多XRD圖譜中并未發(fā)現(xiàn)有雜相峰的存在,同時(shí)各衍射峰的位置也沒有發(fā)生明顯的移動(dòng)(見圖1(b)及圖1(c)中(112)及(332)衍射峰的放大圖). 由于Ga3+和Sb5+的離子半徑相同,因此Ga摻入后化合物的晶格常數(shù)基本沒有變化. 圖2(a)和圖2(b)分別為樣品Cu2.95Ga0.02Sb0.98Se4和Cu2.95Ga0.04Sb0.96Se4的背散射電子圖像,可以確認(rèn)在Ga摻雜量較多時(shí),樣品成分仍然比較均勻,并沒有產(chǎn)生第二相.EDXS測(cè)量的樣品各成分原子比與其名義成分的原子比列于表1,結(jié)果表明Cu,Sb和Se的實(shí)際成分與名義成分接近,高溫反應(yīng)后的各元素成分并無太大變化,同時(shí)對(duì)Se元素的揮發(fā)控制也較好.

表1 Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)名義成分和實(shí)際成分的原子比Tab le 1.NoMinal and actual atoMic contents for Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)detected by EDXS.

圖2 (a)樣品Cu2.95Ga0.02 Sb0.98Se4和(b)樣品Cu2.95Ga0.04 Sb0.96 Se4的背散射電子圖像Fig.2.BSE iMages of the saMp les(a)Cu2.95Ga0.02-Sb0.98Se4 and(b)Cu2.95Ga0.04Sb0.96Se4.

圖3 (網(wǎng)刊彩色)樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)(a)電導(dǎo)率(σ)和(b)Seebeck系數(shù)(S)隨溫度(T)的變化Fig.3. (color on line)TeMperature dependence of(a)electrical conductivities(σ)and(b)Seebeck coeffi cients(S)for Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)saMp les.

圖3(a)為樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02,0.04)的電導(dǎo)率(σ)隨溫度的變化規(guī)律.很明顯,雖然樣品中存在一些Cu空位,能夠提供少量的空穴載流子,但未摻雜Ga的Cu2.95SbSe4樣品的電導(dǎo)率仍然較小,室溫下約為5500 S/m,其電導(dǎo)率隨溫度的變化規(guī)律呈現(xiàn)非簡(jiǎn)并半導(dǎo)體行為.當(dāng)x=0.01時(shí),樣品在室溫下的電導(dǎo)率提高到了12800 S/m.然而,當(dāng)摻入更多Ga時(shí),電導(dǎo)率隨Ga摻雜濃度的增加反而減小.樣品的載流子濃度如表2所列,樣品的載流子濃度隨Ga含量的增加而增大,說明Ga3+取代Sb5+有效地提高了樣品的載流子濃度.另一方面,樣品的空穴遷移率隨Ga摻雜濃度的升高而急劇降低.當(dāng)x=0.01時(shí),樣品的遷移率已經(jīng)降到20 cm2.V?1.s?1以下,這與文獻(xiàn)[27]報(bào)道中In摻雜的情況類似.因此,x＞0.01樣品的電導(dǎo)率降低與載流子遷移率的降低有關(guān).我們利用測(cè)量得到的載流子濃度和Seebeck系數(shù)(見圖3)計(jì)算了價(jià)帶頂?shù)挠行з|(zhì)量.假設(shè)價(jià)帶為單帶拋物線型并且其中的主導(dǎo)散射機(jī)制為聲學(xué)聲子散射,可由以下兩個(gè)公式估算有效質(zhì)量m?[23,29]:

式中kB,h,n,η分別為玻爾茲曼常數(shù)、普朗克常量、載流子濃度和約化費(fèi)米能級(jí)(費(fèi)米能除以kT);Fm(η)為m階FerMi-Dirac積分.計(jì)算結(jié)果如表2所列,x=0.01樣品的空穴有效質(zhì)量是未摻Ga樣品的1.7倍.隨著Ga含量的增加,空穴有效質(zhì)量進(jìn)一步增大.說明遷移率的減小除了與Ga摻雜引入的缺陷有關(guān)之外,還與有效質(zhì)量增大有關(guān).另外,Cu2.95SbSe4樣品的帶隙(Eg)可以通過(6)式[30]進(jìn)行粗略估計(jì),

式中Smax,TSmax分別為最大Seebeck系數(shù)和與之相對(duì)應(yīng)的溫度,e為電子電荷量.計(jì)算得到的帶隙值約為0.28 eV,與文獻(xiàn)[19]報(bào)道的0.29 eV相一致.

另一方面,由圖3(b)可知,未摻雜Ga的樣品其Seebeck系數(shù)隨溫度的升高先增大后減小,呈現(xiàn)非簡(jiǎn)并半導(dǎo)體行為.而當(dāng)摻入了Ga之后,Seebeck系數(shù)隨著溫度升高而增大,轉(zhuǎn)變成為簡(jiǎn)并半導(dǎo)體行為.根據(jù)Mott關(guān)系[6,31,32],Seebeck系數(shù)近似和載流子濃度成反比,隨著Ga摻入量的增多,樣品的載流子濃度逐漸增大,Seebeck系數(shù)依次減小.然而,由于Ga摻雜后空穴的有效質(zhì)量顯著增加,導(dǎo)致Seebeck系數(shù)并沒有隨載流子濃度的增大而迅速下降,因此室溫下所有樣品的Seebeck系數(shù)均維持在200μV.K?1以上.另外載流子濃度的增大還抑制了本征激發(fā),Cu2.95SbSe4的本征激發(fā)溫度約為430 K,x=0.01的樣品本征激發(fā)溫度升高到約550 K,而Ga含量更高的樣品在測(cè)試溫度范圍內(nèi)未出現(xiàn)明顯的本征激發(fā).

圖4為樣品功率因子PF隨溫度的變化關(guān)系.由于具有較合適的電導(dǎo)率和Seebeck系數(shù),相比于其他樣品,x=0.01的樣品在整個(gè)測(cè)試溫度范圍內(nèi)具有最大的功率因子,并在625 K時(shí)達(dá)到了約10 μW/cm.K2,比未摻雜Ga的Cu2.95SbSe4樣品提高了接近一倍.而載流子濃度更大的x=0.02和0.04的兩個(gè)樣品,由于遷移率較小,導(dǎo)致其功率因子小于x=0.01的樣品,最大分別為9μW/cm.K2和8μW/cm.K2,但都大于未摻Ga的樣品.

圖5(a)為樣品總熱導(dǎo)率隨溫度變化的曲線.圖5(b)為晶格熱導(dǎo)率隨溫度變化的曲線.晶格熱導(dǎo)率由總熱導(dǎo)率(κtot)扣除電子熱導(dǎo)率(κe=LσT)得到,即κlattice= κtot? LσT,其中L為洛倫茲常數(shù).利用單帶模型,洛倫茲常數(shù)L可以簡(jiǎn)化為[33]

圖4 (網(wǎng)刊彩色)樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)的PFFig.4. (color on line)TeMperature dependence of power factors for Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)saMp les.

表2 室溫下樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)的載流子濃度(n)、遷移率(μ)、電導(dǎo)率(σ)以及有效質(zhì)量(m*)Tab le 2.RooMteMperature carrier concentrations(n),HallMobilities(μ),electrical conductivities(σ)and eff ectiveMasses for Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)saMp les.

圖5 (網(wǎng)刊彩色)樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02,0.04)的(a)總熱導(dǎo)率(κtot)和(b)晶格熱導(dǎo)率(κlattice),圖(b)中紅色虛線為T?1關(guān)系,黑色虛線為Cahill模型計(jì)算得到的理論最低晶格熱導(dǎo)率Fig.5.(color on line)TeMperature dependence of(a)total therMal conductivity and(b)lattice therMal conductivity for Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)saMp les.In Fig.(b),the red dashed line rep resents the relationship of lattice therMal conductivity and T?1,and the b lack dashed line is the calcu lated lowest therMal conductivity With the CahillModel.

式中kB,e和η分別為玻爾茲曼常數(shù)、電子電荷量以及約化費(fèi)米能級(jí)(費(fèi)米能除以kBT).Fm(η)為m階FerMi-Dirac積分.我們的計(jì)算采用Kim等[34]進(jìn)一步擬合得到的結(jié)果:

其中S為Seebeck系數(shù).從晶格熱導(dǎo)率隨溫度的變化趨勢(shì)來看,基本上符合T?1變化規(guī)律,說明主要的聲子散射機(jī)制為UMklapp過程.但是在高溫下,未摻Ga以及x=0.01樣品的晶格熱導(dǎo)率對(duì)T?1規(guī)律有較大偏離,這是由樣品的雙極擴(kuò)散導(dǎo)致.隨著摻Ga濃度的進(jìn)一步增大,載流子的雙極擴(kuò)散得到有效抑制,因此x＞0.01樣品高溫下的晶格熱導(dǎo)率與T?1規(guī)律符合較好.此外,如圖5所示,Ga的摻入對(duì)熱導(dǎo)率的影響不大,這與文獻(xiàn)[26]報(bào)道的A l摻雜的情況類似.但是在高溫區(qū),Ga摻雜引入的點(diǎn)缺陷對(duì)高頻聲子有較強(qiáng)的散射作用,導(dǎo)致?lián)紾a樣品的高溫晶格熱導(dǎo)率有所降低.但是所有樣品的晶格熱導(dǎo)率仍然明顯高于Zhang等[35]通過Cahill模型計(jì)算得到的理論最低晶格熱導(dǎo)率0.5W.m?1.K?1.因此Cu3SbSe4化合物的晶格熱導(dǎo)率還有進(jìn)一步降低的空間.圖6為樣品的斷面SEM形貌圖.對(duì)比發(fā)現(xiàn),未摻Ga樣品的晶粒大小較為均勻,約為15μm左右(如圖6(a)所示).當(dāng)摻入Ga之后,樣品的晶粒尺寸變得不均勻,在較大晶粒之間出現(xiàn)5μm以下的較小晶粒.但是,所有樣品的孔洞數(shù)量并未出現(xiàn)較大變化,因此樣品的相對(duì)密度大致相同,均為97%左右(如表3所列).所以,樣品的微結(jié)構(gòu)對(duì)其熱電性能沒有明顯影響.

圖7為樣品的ZT值,摻Ga樣品的ZT值均大于未摻Ga樣品,其中x=0.02樣品由于高溫?zé)釋?dǎo)率降低較大,因此其ZT最大,664 K時(shí)約為0.53.而功率因子最大的x=0.01樣品,由于熱導(dǎo)率相對(duì)較大,最終其高溫區(qū)的熱電性能與x=0.02的樣品相當(dāng),664 K時(shí)的ZT值約為0.52,比未摻Ga的樣品提高了約50%.圖7中我們也給出了部分文獻(xiàn)報(bào)道的結(jié)果,通過對(duì)比發(fā)現(xiàn),Sn摻雜[22]對(duì)Cu3SbSe4熱電性能的提升作用較為顯著,其ZT在675 K時(shí)達(dá)到了約0.75.而第三主族元素(A l,Ga,In)的摻雜雖然能優(yōu)化材料的電輸運(yùn)性能,但對(duì)熱導(dǎo)率沒有明顯影響,因此樣品ZT值的提高有限.

表3 樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)的相對(duì)密度Tab le 3.Relative densities for Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)saMp les.

圖6 樣品Cu2.95GaxSb1?xSe4(x=0,0.01,0.02,0.04)的斷面SEM形貌圖Fig.6.SEMiMages of fractu re su rfaces for Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)saMp les.

圖7 (網(wǎng)刊彩色) 樣品Cu2.95GaxSb1?xSe4(x= 0,0.01,0.02和0.04)的ZT值與Cu3Sb0.975Sn0.025Se4[22],Cu3Sb0.97A l0.03 Se4[26]及Cu3 Sb0.997 In0.003Se4[27]化合物的比較,圖中ZT值測(cè)量誤差均為10%Fig.7. (color on line)TeMperatu re dependence of ZT for Cu2.95GaxSb1?xSe4(x= 0,0.01,0.02 and 0.04)saMp les coMpared With Cu3Sb0.975Sn0.025Se4[22],Cu3Sb0.97A l0.03 Se4[26] and Cu3Sb0.997 In0.003 Se4[27]coMpounds.TheMeasureMent error is 10%for ZT(error bar).

4 結(jié) 論

我們運(yùn)用熔融-淬火方法制備了Cu2.95GaxSb1?xSe4(x=0,0.01,0.02和0.04)樣品,Ga摻雜有效地增大了樣品的載流子濃度,并且抑制了本征激發(fā).x=0.01時(shí),樣品的電導(dǎo)率達(dá)到最大,625 K時(shí)的功率因子達(dá)到10μW/cm.K2.但是隨著載流子濃度的增大,樣品的載流子遷移率急劇下降,導(dǎo)致具有更大載流子濃度的樣品的電導(dǎo)率并未得到進(jìn)一步提升.從熱導(dǎo)率的變化結(jié)果來看,高溫下,Ga摻雜可以有效降低雙極擴(kuò)散對(duì)熱導(dǎo)率的貢獻(xiàn),同時(shí)引入的點(diǎn)缺陷對(duì)高頻聲子有一定的散射作用,因此可以降低樣品高溫區(qū)的熱導(dǎo)率.最終該體系的在664 K時(shí)達(dá)到最大ZT值0.53,比未摻Ga樣品提高了近50%.基于本文研究結(jié)果及文獻(xiàn)[26,27]報(bào)道,可以得知第三主族元素A l,Ga和In的摻雜對(duì)Cu3SbSe4的熱電性能具有相似的作用,三種元素對(duì)Sb的替位摻雜均可以作為調(diào)控Cu3SbSe4載流子濃度的有效手段.但是這三種元素的摻雜對(duì)材料的熱導(dǎo)率沒有明顯影響,樣品ZT值的提高有限,因此還需要引入雙元素?fù)诫s或者微結(jié)構(gòu)調(diào)控等手段進(jìn)一步降低樣品的熱導(dǎo)率.

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PACS:72.20.Pa,72.10.Fk,61.72.U–,65.40.–bDOI:10.7498/aps.66.167201

*Pro ject supported by the National Natural Science Foundation of China(G rant Nos.51371194,51172276,51632005).

?Corresponding author.E-Mail:jun luo@shu.edu.cn

?Corresponding au thor.E-Mail:wqzhang@shu.edu.cn

E ff ect of Ga dop ing on the therMoelectric perforMance of Cu3SbSe4?

Chen Luo-Na Liu Ye-Feng Zhang Ji-Ye Yang Jiong Xing Juan-Juan Luo Jun?Zhang Wen-Qing?

(School ofMaterial Science and Engineering,Shanghai University,Shanghai 200444,China)

20 Ap ril 2017;revised Manuscrip t

9 June 2017)

The Cu3SbSe4coMpound is an environMentally friend ly and low-cost Medium-teMperature therMoelectric Material,which is featured by its loWtherMal conductivity.The disadvantage of this coMpound lies in its intrinsic poor electrical transport property.In order to iMprove the electrical conductivity of Cu3SbSe4,in this work we are to increase its carrier concentration by one to two orders ofMagnitude though eleMental doping.The saMp le coMposition of Cu2.95GaxSb1?xSe4is designed to increase the hole carrier concentration by introducing Cu vacancies and substituting Ga3+for Sb5+.The Cu2.95GaxSb1?xSe4(x=0,0.01,0.02 and 0.04)saMp les are p repared by Melting-quench Method.The X-ray diff raction analysis indicates that the obtained saMp les are of single-phase With the tetragonal faMatinite structure,and the energy-dispersive X-ray spectroscopy results shoWthat the actual compositions of the saMp les are very close to their noMinal coMpositions.The eff ect of Ga doping on the therMoelectric perforMance of Cu3SbSe4coMpound is investigated systeMatically by electrical and therMal transport p roperty MeasureMents.According to our experimental results,the hole concentration of the saMp le is effi ciently increased by substituting Sb With a small amount of Ga(x=0.01),which can not only substantially iMp rove the electrical conductivity but also supp ress the intrinsic excitation of the saMp le.The MaximuMpower factor reaches 10 μW/cm.K2at 625 K for the Ga doped saMp le With x=0.01,which is nearly tWice asmuch as that of the saMp le free of Ga.A lthough the carrier concentration further increases With increasing Ga content,the hole Mobility decreases d raMatically With the Ga content increasing due to the increased hole eff ectivemass and point defect scattering.Thus,the electrical transport p roperties of the saMp les deteriorate at higher Ga content,and theMaximuMpower factors for the saMp les With x=0.02 and 0.04 reach 9 and 8 μW/cm.K2at 625 K,respectively.The lattice therMal conductivities of the saMp les basically coMp ly With the T?1relationship,suggesting the phonon U-process is the doMinant scattering mechanisMin our saMp les.For the saMp les With x=0 and 0.01,the lattice therMal conductivities at high teMperature deviate slightly froMthe T?1curve due to the presence of intrinsic excitation.However,these deviations are eliMinated for the saMp les With x=0.02 and 0.04 because the bipolar eff ect is eff ectively suppressed With the increasing of Ga content.Thus,Ga doping can reduce the bipolar therMal conductivity at high teMperature by increasing the hole carrier concentration.FurtherMore,the point defects introduced by Ga doping can also enhance the scattering of high-frequency phonons,leading to slightly reduced lattice thermal conductivities of Ga-doped saMp les at higher teMperature.Finally,a maximuMZT value of 0.53 at 664 K is achieved in Ga-doped saMp le,which is 50%higher than that of the saMp le free of Ga.

Ga doping,Cu3SbSe4,thermoelectric performance

10.7498/aps.66.167201

?國(guó)家自然科學(xué)基金(批準(zhǔn)號(hào):51371194,51172276,51632005)資助的課題.

?通信作者.E-Mail:jun luo@shu.edu.cn

?通信作者.E-Mail:Wqzhang@shu.edu.cn

?2017中國(guó)物理學(xué)會(huì)C h inese P hysica l Society

http://Wu lixb.iphy.ac.cn