氧化鑭摻雜鈮酸鉀鈉陶瓷的電、光性能研究

肖舒琳, 戴中華, 李定妍, 張凡博, 楊利紅, 任曉兵

氧化鑭摻雜鈮酸鉀鈉陶瓷的電、光性能研究

肖舒琳1, 戴中華1, 李定妍1, 張凡博1, 楊利紅1, 任曉兵2

(1. 西安工業(yè)大學(xué) 光電工程學(xué)院, 陜西省薄膜技術(shù)與光學(xué)檢測(cè)重點(diǎn)實(shí)驗(yàn)室, 西安 710021; 2. 西安交通大學(xué) 前沿技術(shù)研究院, 西安 710049)

鈮酸鉀鈉(K0.5Na0.5NbO3, KNN)基陶瓷具有充放電速度快、透明度高、應(yīng)用溫度范圍寬、使用壽命長(zhǎng)等優(yōu)點(diǎn), 在脈沖功率器件等領(lǐng)域具有廣闊的應(yīng)用前景。通過(guò)改性技術(shù)提高鈮酸鉀鈉基陶瓷的電、光性能是該方向的研究熱點(diǎn)。本研究采用固相法制備0.825(K0.5Na0.5)NbO3-0.175Sr1–3x/2La(Sc0.5Nb0.5)O3(=0, 0.1, 0.2, 0.3)陶瓷(簡(jiǎn)稱0.825KNN- 0.175SLSN), 研究La2O3摻雜對(duì)其相結(jié)構(gòu)、微觀形貌、光學(xué)、介電、鐵電及儲(chǔ)能性能的影響。研究結(jié)果表明: 0.825KNN- 0.175SLSN陶瓷具有高對(duì)稱性的偽立方相結(jié)構(gòu); 隨著La2O3摻雜量增大, 陶瓷的平均晶粒尺寸減小, 相變溫度(m)及飽和極化強(qiáng)度(max)增大, 達(dá)到峰值后下降。在=0.3時(shí), 該體系陶瓷表現(xiàn)出優(yōu)異的透明性, 在可見(jiàn)光波長(zhǎng)(780 nm)及近紅外波長(zhǎng)(1200 nm)范圍內(nèi)透過(guò)率分別達(dá)65.2%及71.5%, 同時(shí)實(shí)現(xiàn)了310 kV/cm的擊穿場(chǎng)強(qiáng)和1.85 J/cm3的可釋放能量密度。

鈮酸鉀鈉; 無(wú)鉛透明陶瓷; 透過(guò)率; 儲(chǔ)能性能

隨著脈沖功率技術(shù)的快速發(fā)展和元件透明化需求的增加, 具有優(yōu)異儲(chǔ)能特性的無(wú)鉛透明鐵電陶瓷作為脈沖功率系統(tǒng)的關(guān)鍵元件, 被廣泛應(yīng)用于航天航空、定向武器和新能源汽車(chē)等領(lǐng)域[1-4]。目前常見(jiàn)的儲(chǔ)能材料體系有NaNbO3(NN)體系、K0.5Na0.5NbO3(KNN)體系、BaTiO3(BT)體系與Bi0.5Na0.5TiO3(BNT)體系等。上述材料中, KNN基陶瓷材料具有較高的居里溫度、穩(wěn)定的高壓電系數(shù)、易固溶、缺陷容忍度高等優(yōu)點(diǎn), 是易于實(shí)現(xiàn)光學(xué)、電學(xué)以及機(jī)械性能耦合的多功能材料[5-7]。純KNN陶瓷的剩余極化強(qiáng)度r較大, 飽和極化強(qiáng)度與剩余極化強(qiáng)度差(max–r)小于5 μC/cm2, 且擊穿場(chǎng)強(qiáng)b<40 kV/cm, 導(dǎo)致其不能作為優(yōu)良的儲(chǔ)能介質(zhì)材料[8]。此外, KNN陶瓷在室溫下為高對(duì)稱性的正交相結(jié)構(gòu), 粒徑為4～5 μm[9], 難以采用普通的燒結(jié)方法制成透明陶瓷[10-11]。

為了改善KNN材料的電學(xué)及光學(xué)性能, 研究者嘗試通過(guò)稀土元素?fù)诫s改性基體材料。Lu等[12]通過(guò)在Bi0.5Na0.5TiO3-BaTiO3材料中摻雜適量的La和Zr元素, 最終得到了可利用儲(chǔ)能密度rec= 1.21 J/cm3。Wang等[13]對(duì)BNT基陶瓷改性, 設(shè)計(jì)了[(Bi0.5Na0.5)0.94Ba0.06]La(1–x)ZrTiO3儲(chǔ)能陶瓷, 其具有高飽和極化強(qiáng)度(max=37.5 μC/cm2), 并表現(xiàn)出雙電滯回線形狀, 可利用儲(chǔ)能密度rec提高至1.58 J/cm3。為實(shí)現(xiàn)多晶陶瓷材料的透明性, Ren等[14]通過(guò)在K0.5Na0.5NbO3中引入SrZrO3作為第二組元, 將晶粒尺寸降至0.19 μm, 從而使(1–)K0.5Na0.5NbO3-SrZrO3陶瓷獲得較高的光學(xué)透明性(～68%)。Zhang等[15]通過(guò)在KNN基陶瓷中固溶第二組元(K0.7Bi0.3)NbO3, 使其在晶界處聚集來(lái)抑制晶粒生長(zhǎng), 利用固相反應(yīng)法制備的0.85KNN-0.15KBN透明陶瓷在近紅外光波長(zhǎng)范圍內(nèi)透光率達(dá)到83.3%。Heartling等[16]通過(guò)熱壓燒結(jié)技術(shù), 在鋯鈦酸鉛(PZT)陶瓷基體中摻入La元素, 制備出鋯鈦酸鉛鑭(PLZT)透明陶瓷, 大大提高了鉛基陶瓷的透明度。Song等[17]在PMN-PT馳豫鐵電陶瓷中加入La元素后制備了高透明度的陶瓷, 當(dāng)摻雜量為4%, 厚度為0.5 mm時(shí), 陶瓷透光率在可見(jiàn)光范圍內(nèi)接近70%。

本研究通過(guò)稀土元素異價(jià)離子取代方法, 在0.825(K0.5Na0.5)NbO3-0.175Sr(Sc0.5Nb0.5)O3陶瓷中摻入La2O3。采用傳統(tǒng)固相反應(yīng)法制備0.825(K0.5Na0.5)NbO3-0.175Sr1–3x/2La(Sc0.5Nb0.5)O3(= 0, 0.1, 0.2, 0.3)陶瓷, 簡(jiǎn)稱0.825KNN-0.175SLSN陶瓷, 研究摻雜La2O3含量對(duì)0.825KNN-0.175SLSN陶瓷相結(jié)構(gòu)、微觀形貌、光學(xué)、介電、鐵電及儲(chǔ)能性能的影響規(guī)律。

1 實(shí)驗(yàn)方法

1.1 樣品制備

以分析純K2CO3(99.5%)、Na2CO3(99.8%)、Nb2O5(99.5%)、Sr2CO3(99%)、Sc2O3(99.9%)和La2O3(99%)為原料, 采用傳統(tǒng)固態(tài)反應(yīng)法制備0.825KNN-0.175SLSN陶瓷(=0, 0.1, 0.2, 0.3)。根據(jù)化學(xué)計(jì)量比進(jìn)行稱料, 將混合粉料進(jìn)行一次球磨, 以2～5 mm的鋯球?yàn)榻橘|(zhì), 在酒精中球磨18 h。將料漿置于培養(yǎng)皿中, 在80 ℃烘干后進(jìn)行篩料。將得到的粉料置于密閉的氧化鋁坩堝中在950 ℃保溫5 h進(jìn)行預(yù)燒, 再進(jìn)行10 h二次球磨。干燥后, 將粉料與質(zhì)量百分比5%的聚乙烯醇水溶液均勻混合。為了使粘結(jié)劑充分?jǐn)U散, 將混合后的粉料壓制成坯體后放置12 h?；旌戏哿显?50 MPa下壓制成12 mm×1 mm的圓柱生坯。壓制的生坯樣品在600 ℃下保溫5 h排膠后, 再在1200～1300 ℃燒結(jié)5 h。為了獲得高的擊穿場(chǎng)強(qiáng), 本研究對(duì)燒結(jié)后的樣品進(jìn)行打磨拋光處理, 使其表面平行光滑, 厚度約為0.15 mm。采用絲網(wǎng)印刷方法在樣品表面涂覆銀漿, 800 ℃燒制20 min后得到銀電極。

1.2 性能測(cè)試

采用Archimedes排水法測(cè)試樣品密度; 采用Ｘ射線衍射儀(XRD, D8 Advance, Bruker, Germany)和掃描電子顯微鏡(SEM, Quanta 250F, FEI, USA)測(cè)試燒結(jié)后樣品的相結(jié)構(gòu)及微觀形貌; 采用LCR電橋(E4980A, Aglient, USA)在–150～150 ℃溫度范圍以及1～1000 kHz的頻率下測(cè)試樣品的介電常數(shù); 采用分光光度計(jì)(UV-2550, Tokyo, Japan)測(cè)試樣品的透過(guò)率, 測(cè)試波長(zhǎng)范圍為400～1200 nm。采用鐵電測(cè)試儀(Premier II, Radiant, USA)測(cè)試樣品室溫下電滯回線, 測(cè)試頻率為5 Hz。

2 結(jié)果與討論

2.1 0.825KNN-0.175SLSN陶瓷的結(jié)構(gòu)分析

材料的致密度越高, 材料內(nèi)部的氣孔雜質(zhì)越少, 可以降低材料氣孔對(duì)于光線的吸收, 從而提高光線透過(guò)率[18-20]; 還可有利于提高的擊穿場(chǎng)強(qiáng), 從而獲得較大的儲(chǔ)能密度。圖1為0.825KNN-0.175SLSN陶瓷樣品在室溫下測(cè)得的密度–摻雜量關(guān)系曲線。由圖可知隨著La2O3含量增大, 0.825KNN-0.175SLSN陶瓷的密度先降低后逐漸提高, 在=0.3處陶瓷密度最大。

圖2為0.825KNN-0.175SLSN陶瓷的XRD圖譜, 可以發(fā)現(xiàn)XRD衍射譜無(wú)雜峰, 均呈單一的鈣鈦礦結(jié)構(gòu)。由此可見(jiàn), 摻入La2O3均形成了單一結(jié)構(gòu)固溶體。所有樣品在2=45°附近只顯示(200)峰, 不存在三方或四方的晶格畸變, 表明樣品均為偽立方相結(jié)構(gòu)[21-22]。由于偽立方結(jié)構(gòu)的高對(duì)稱性, 大大降低了光在傳播過(guò)程中由于衍射和雙折射所產(chǎn)生的光損耗, 進(jìn)而提高光學(xué)透過(guò)率。

圖3為0.825KNN-0.175SLSN陶瓷樣品的表面掃描電鏡照片。從圖中可以觀察到各個(gè)組分0.825KNN-0.175SLSN陶瓷的晶粒結(jié)晶性好, 晶粒堆疊生長(zhǎng), 晶界清晰。當(dāng)=0.2時(shí), 晶粒間具有較明顯的氣孔, 會(huì)對(duì)樣品的致密度產(chǎn)生一定影響, 從而導(dǎo)致?lián)舸﹫?chǎng)強(qiáng)降低以及入射光發(fā)生散射, 最終影響樣品的儲(chǔ)能及透光性能。圖3的插圖為0.825KNN- 0.175SLSN陶瓷的粒徑分布圖, 可以發(fā)現(xiàn)摻雜La2O3在一定程度上抑制了0.825KNN-0.175SLSN陶瓷的晶粒生長(zhǎng)。當(dāng)=0.3時(shí), 平均晶粒尺寸為0.24 μm。一般來(lái)說(shuō), 透明儲(chǔ)能陶瓷的晶粒分布均勻, 可降低入射光的損失并提高樣品的擊穿場(chǎng)強(qiáng), 從而提高光學(xué)透過(guò)率及儲(chǔ)能密度。

圖1 0.825KNN-0.175SLSN陶瓷密度與La含量的關(guān)系圖

圖2 0.825KNN-0.175SLSN陶瓷在室溫下2θ的XRD譜圖

圖3 0.825KNN-0.175SLSN陶瓷室溫下自然表面的掃描電鏡照片

(a)=0; (b)=0.1; (c)=0.2; (d)=0.3

2.2 0.825KNN-0.175SLSN陶瓷的光學(xué)性能分析

在0.825KNN-0.175SLSN體系樣品中,=0.3的陶瓷的透明度最高。圖4(a)為400～1200 nm波長(zhǎng)范圍內(nèi)0.825KNN-0.175SLSN陶瓷(=0, 0.3)的直線透過(guò)率光譜圖。圖4(a)的插圖為0.825KNN-0.175SLSN陶瓷(=0, 0.3)樣品的照片。0.825KNN-0.175SLSN陶瓷經(jīng)打磨至0.3 mm并拋光后,=0.3陶瓷的光學(xué)透過(guò)率在可見(jiàn)光波長(zhǎng)780 nm處為65.2%(較=0時(shí)的60.2%提升了8.3%), 在近紅外波長(zhǎng)1200 nm處的透過(guò)率達(dá)71.5%。與KNN基儲(chǔ)能陶瓷的研究報(bào)道[23-25]比較, 0.825KNN-0.175SLSN (=0.3)陶瓷具有更優(yōu)異的透明性, 有望取代鉛基透明儲(chǔ)能材料。

當(dāng)入射光進(jìn)入陶瓷材料內(nèi)部時(shí), 會(huì)激發(fā)具有一定能量的電子從價(jià)帶躍遷到導(dǎo)帶, 造成光能量損失。增大材料的禁帶寬度會(huì)抑制電子發(fā)生躍遷, 從而有利于提高材料的透明度。禁帶寬度g可通過(guò)Tauc方程得出, 如下式[26]:

其中, 吸收率和光子頻率可以根據(jù)以下公式獲得:

其中,為普朗克常量(4.1357×10–15eV),為常數(shù),為樣品厚度,為光速(3×108m/s),為透過(guò)率,為波長(zhǎng)。

通過(guò)對(duì)圖4(a)中0.825KNN-0.175SLSN陶瓷樣品的光學(xué)透過(guò)率曲線進(jìn)行擬合計(jì)算, 可得圖4(b), 由圖可知, 當(dāng)=0.3時(shí)0.825KNN-0.175SLSN陶瓷的禁帶寬度g=2.95 eV。

2.3 0.825KNN-0.175SLSN陶瓷的介電性能分析

圖5(a～d)為0.825KNN-0.175SLSN陶瓷的介電性能–溫度關(guān)系圖。隨著值增大, 介電常數(shù)峰逐漸從一個(gè)轉(zhuǎn)變?yōu)閮蓚€(gè)。當(dāng)=0.2和0.3時(shí), 出現(xiàn)的兩個(gè)介電常數(shù)峰在–75 ℃和100 ℃附近, 分別對(duì)應(yīng)正交相向四方相的相變以及四方相向立方相的相變, 這也印證了XRD的測(cè)試結(jié)果, 室溫下0.825KNN- 0.175SLSN陶瓷均為偽立方的相結(jié)構(gòu)[27]。0.825KNN- 0.175SLSN陶瓷在室溫下的介電損耗低于0.03, 有利于獲得優(yōu)異的儲(chǔ)能性能。圖5(e)為0.825KNN- 0.175SLSN陶瓷在1 kHz下測(cè)試的最大介電常數(shù)對(duì)應(yīng)的溫度(m)與介電常數(shù)值(m)的關(guān)系曲線, 隨著增大,m呈現(xiàn)升高的趨勢(shì),m在950～1100之間。

2.4 0.825KNN-0.175SLSN陶瓷的鐵電性能分析

圖6為室溫下0.825KNN-0.175SLSN陶瓷樣品在150 kV/cm, 5 Hz下測(cè)得的不同組分樣品的單極曲線, 由圖可知, 所有組分的樣品都為細(xì)電滯回線, 顯現(xiàn)出弛豫鐵電體的特征。為了直觀觀察和分析0.825KNN-0.175SLSN陶瓷樣品極化強(qiáng)度的變化情況, 根據(jù)圖6中的單極電滯回線進(jìn)行統(tǒng)計(jì)。

圖7為0.825KNN-0.175SLSN陶瓷的max和r與摻雜含量的關(guān)系曲線。由圖可知, 陶瓷樣品的r均小于2 μC/cm2,r越小, 越有利于提高儲(chǔ)能效率。隨著La含量增大,max呈增大趨勢(shì)。當(dāng)從0增至0.2時(shí), 0.825KNN-0.175SLSN陶瓷max值逐漸從10.06 μC/cm2增大至13.12 μC/cm2, 可見(jiàn)摻雜適量的La元素可以使0.825KNN-0.175SLSN陶瓷max提高,有利于提高材料的儲(chǔ)能密度。

圖5 0.825KNN-0.175SLSN陶瓷樣品的介電性能–溫度關(guān)系圖(a～d)和0.825KNN-0.175SLSN陶瓷的Tm, εm與La摻雜含量關(guān)系圖(e)

圖6 0.825KNN-0.175SLSN陶瓷在150 kV/cm電場(chǎng)下的單極P-E曲線

Colorful figures are available on website

圖7 不同La摻雜含量陶瓷的Pmax和Pr

影響儲(chǔ)能密度的另一個(gè)重要因素是陶瓷樣品的擊穿電場(chǎng)強(qiáng)度b[9,28]。0.825KNN-0.175SLSN陶瓷在擊穿場(chǎng)強(qiáng)下的單極電滯回線如圖8(a～d)所示。鐵電材料的儲(chǔ)能密度和儲(chǔ)能效率可通過(guò)以下公式獲得[29-31]:

其中,rec、、max、r、、分別表示陶瓷樣品可利用儲(chǔ)能密度、儲(chǔ)能密度、飽和極化強(qiáng)度、剩余極化強(qiáng)度、外加電場(chǎng)和儲(chǔ)能效率。通過(guò)對(duì)圖8(a～d)所得的單極電滯回線進(jìn)行積分計(jì)算, 得到圖8(e)所示的、rec隨值的變化曲線, 圖8(f)為b、隨值的變化曲線。隨著La含量增大, 不同組分陶瓷的rec和值呈現(xiàn)逐漸減小之后再增大的趨勢(shì)。由于氣孔和擊穿場(chǎng)強(qiáng)的限制, 在=0.2時(shí)儲(chǔ)能密度最低,=1.14 J/cm3及rec=0.95 J/cm3。0.825KNN- 0.175SLSN(=0.3)陶瓷具有最優(yōu)的儲(chǔ)能密度= 2.25 J/cm3及rec=1.85 J/cm3。

3 結(jié)論

本研究采用稀土元素La摻雜改性0.825(K0.5Na0.5)NbO3-0.175Sr(Sc0.5Nb0.5)O3陶瓷。摻雜后0.825(K0.5Na0.5)NbO3-0.175Sr1–3x/2La(Sc0.5Nb0.5)O3(=0, 0.1, 0.2, 0.3)陶瓷均具有單一的純鈣鈦礦結(jié)構(gòu), 摻雜La元素并未改變基體材料的相結(jié)構(gòu), 均為高對(duì)稱性的偽立方相, 并在一定程度上抑制晶粒生長(zhǎng), 減小晶粒尺寸。隨著La摻雜量增大, 0.825KNN-0.175SLSN陶瓷飽和極化強(qiáng)度max呈現(xiàn)增大的趨勢(shì)。在=0.3時(shí), 0.825KNN-0.175SLSN陶瓷具有優(yōu)異的透明性, 在可見(jiàn)光波長(zhǎng)780 nm及近紅外波長(zhǎng)1200 nm處透過(guò)率分別達(dá)65.2%及71.5%, 同時(shí)實(shí)現(xiàn)了最佳的儲(chǔ)能特性:=2.25 J/cm3、rec= 1.85 J/cm3、=81.9%。0.825KNN-0.175SLSN陶瓷是有望取代鉛基材料作為透明儲(chǔ)能介質(zhì)材料。

圖8 0.825KNN-0.175SLSN陶瓷在擊穿場(chǎng)強(qiáng)下的單極P-E曲線(a～d), 0.825KNN-0.175SLSN陶瓷的W、Wrec與x的關(guān)系曲線(e), 0.825KNN-0.175SLSN陶瓷的η和Eb與x的關(guān)系曲線(f)

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Electrical and Optical Property of Lanthanum Oxide Doped Potassium Sodium Niobate Ceramics

XIAO Shulin1, DAI Zhonghua1, LI Dingyan1, ZHANG Fanbo1, YANG Lihong1, REN Xiaobing2

(1. Shaanxi Province Key Laboratory of Thin Films Technology & Optical Test, School of Optoelectronic Engineering, Xi'an Technological University, Xi'an 710021, China; 2. Frontier Institute of Science and Technology, Xi'an Jiaotong University, X'ian 710049, China)

Potassium sodium niobate (K0.5Na0.5NbO3, KNN) based ceramics can be widely used for pulsed power systems due to their fast charge-discharge rate, high transparency, wide range of working temperature, and long cycle life.Improving the electrical and optical property of KNN-based ceramics through modification is a research hotspot in this field. 0.825(K0.5Na0.5)NbO3-0.175Sr1–3x/2La(Sc0.5Nb0.5)O3(=0, 0.1, 0.2, 0.3) (0.825KNN- 0.175SLSN) ceramics were synthesized by solid state method. The effect of La2O3doping on the phase structure, microstructure, optical property, dielectric property, ferroelectric property and energy storage property of the ceramic was studied. The results indicated that the structure of 0.825KNN-0.175SLSN ceramics was pseudo-cubic phase with high symmetry. With increment of La2O3content, the average grain size of 0.825KNN-0.175SLSN ceramics decreased, and the phase transition temperature (m) and saturation polarization intensity (max) increased and then decreased. 0.825KNN-0.175SLSN ceramics exhibit excellent transparency at=0.3, the transmittance in the visible wavelength (780 nm) and near-infrared wavelength (1200 nm) ranges reaches 65.2% and 71.5%, respectively. The dielectric breakdown strength of 310 kV/cm and a recoverable energy density of 1.85 J/cm3are achieved at=0.3.

potassium sodium niobate; lead-free transparent ceramics; transmittance; energy storage property

1000-324X(2022)05-0520-07

10.15541/jim20210297

TQ174

A

2021-05-11;

2021-07-09;

2021-08-20

國(guó)家自然科學(xué)基金(51831006, 51431007); 陜西省科技計(jì)劃(2020GY-311); 西安市智能兵器重點(diǎn)實(shí)驗(yàn)室基金(2019220514SYS020CG042)

National Natural Science Foundation of China (51831006, 51431007); Science and Technology Project of Shaanxi Province (2020GY-311); Xi’an Key Laboratory of Intelligence (2019220514SYS020CG042)

肖舒琳(1998–), 女, 碩士研究生. E-mail: 1319643700@qq.com

XIAO Shulin (1998–), female, Master candidate. E-mail: 1319643700@qq.com

戴中華, 教授. E-mail: zhdai@mail.xjtu.edu.cn

DAI Zhonghua, professor. E-mail: zhdai@mail.xjtu.edu.cn