Nguyen Van Dang vd cs Tap chi KHOA HOC & CONG NGHE 78(02): 39 - 44
ANH Hl/ONG CUA SlT THAY THE Fe CHO Ti LEN CAU TRUC VA TINH C H A T D I E N TlT CUA BaTiOj
, .. , , Nguyen Van Dang', Nguyen Khac Hiing , Ngo Thj Lan', VQ Dinh Lam" va Le Van Hong' Trudng Dgi hgc Khoa hgc. DH Thai Nguyen ']'ien Khoa hgc vat lieu. ]'ieii KH&CN I'iel Nam
TOM TAT
He vat lieu BaTii.^FexOi (x = 0,0 ^0,03) da dugc tong hgp bang phuong phap phan ung pha rJn.
Mac dii Fe dugc thay the mot phan rit nho cho Ti trong cau true BaTiOj nhung da anh hudng manh len cau true tinh the, pho tan xa Raman va cac tinh chat dien, tii' cua hgp ch§t nay. KSt qua cho thay cau triic tinh the ciia he chuyen tu tii giac sang luc giac ngay d nhiet do phong. Pho tan xa Raman ciia he thay doi va xuat hien mot dinh moi gan 640 cm' khi ham lugng Fethay the khoang 2% cho Ti. Ham lugng Fe^* tang lam cho be rong dai cam giam con do din va tu ti'nh ciia he tang.
Moi lien he giua cau triic, tinh chat quang, dien va tu cQng dugc thao luan trong bao cao nay.
Tix khoa: BaTl/.^Fe^O}, sal dien, sal tir, nhieu xg tia X, pho Raman, phd hap thu, multlferrole
M6DAU
Vai cau true perovskite dac trung (ABO3), vat lieu BaTi03 chua dung nhieu tinh chat ly thii ve tinh sat dien (dien moi, ap dien...) va da dugc dua vao ung dung trong mpt so thiet bj ciia nhieu nganh ky thuat [1-3,10]. Gan day, CO nhieu cong trinh nghien ciiu xet tai viec pha tap cac nguyen to vao vi tri ciia Ba hoac Ti, lam cho tinh chat ciia vat lieu da dang va thu vi hon rat nhieu. Khi pha tap cac nguyen to CO til- tinh nhu Fe, Mn, Ni...vao vi tri cua Ti khi do trong vat lieu dong ton tai hai phan cue dien va phan cue tii-, nghTa la vat lieu dong bieu bien ea tinh chat sat ti'r va sat dien [3,11,12]. Day la mot huong nghien cuu hien thu hut su chu y cua cac nha khoa hoc ca trong nghien euu ly thuySt va iing dung trong cac thiSt bj hien dai nhu: kha nang thu nho linh kien, tang mat do linh kien, tang toe do boat dong va md ra kha nang che tao cac linh kien t6 hop nhilu chuc nang tren cimg mot chip. Trong bao cao nay, chiing toi trinh bay anh huang ciia su pha tap Fe len su chuyen pha c5u trde tinh thi va tinh chat dien tii- ciia vat lieu BaTiOi.
THUC NGHIEM
Cae mill gdm Ba(Ti|_,FeOO.i (0 < x < 0.03) dugc chi tao bSng phuang phap phan img pha
Email: iivdangsptn'ayahoo.com
ran voi nhiet do nung thieu ket la 1300°C trong 5 gid. Do sach pha va cau triic tinh the eiia mau dupe kiem tra bang phuong phap nhieu xa tia X tren nhieu xa ke SIEMENS D5000. Cac phep do tan xa Raman dupe thuc hien tren he Micro Raman LABRAM 1B vdi dau thu CCD trong vung 100 - 1000 cm"' d nhiet dp phdng. Tinh chat quang dupe khao sat thdng qua phep do phd hap thu trong viing budc sdng tir 200 den 1200 nm tren he Jasco 670 UV. Phan thuc cua hang sd dien mdi duac do d nhiet dp phdng trong khoang tan sd tir 10 Hz din 1.3 MHz tren he HP4192A.
Dudng til- tre dupe do theo nguyen ly tir ke mau rung (VSM) trong tu trudng 1 Tesia tren he PPMS-6000 ciia hang Quantum Design.
KET QUA v A THAO L U A N
Gian dd nhieu xa tia X cua eac mau dupe trinh bay tren hinh 1. Ket qua cho thay cac mau hoan toan sach pha va cd cau true da tinh the. Vdi ham lupng Fe thay the x = 0.00 -;- 0.01 vat lieu ed cau triic tii- giac (tetragonal), cdn cac mau vdi x = 0.02 va 0.03 bieu hien sir ddng tdn tai ca hai loai cau triic tit giac va luc giac (hexagonal). Mau cd x = 0.02 cau triic luc giac da bat dau hinh thanh nhung chiem ty le nhd, cau triic tu giac van chiem ty le rat Idn. Sir chuyen cau triic cua he dugc the hien rat rd tren phd nhieu xa tia X, cac vach nhieu xa ehinh cua cae mau vdi x = 0.00 ^ 0.01 tai
39
N2u\en Van Dans vd cs Tap chi KHOA HOC & CONG NGHE 78(02): 39-44 cac vi tri gdc 26 bSng 31.5^^; 38.8 ...la cac
\ach don trong khi cae vach d vj tri tuong ling ddi vdi cac mau cd x = 0.02 ^ 0.03 lai la cac \'ach kep. Dong thdi tai x = 0.02 bat dau xuk hien cae vach dac trung cua cau triic luc giac tai cac vi tri adc 26 bans 26.2 ; 41.2 : 49. iV'..
Hinh 1. Gian do nhilu xa tia X ciia cac mau Ba(Ti,.,Fe,)O3(0<x<0.03)
Quan sat tren gian dd nhieu xa tia X cdn cho thay khi ndng dp Fe tang cac dinh phd cd xu hudng djch chu\en \'e phia gdc 26 nhd, nghTa la cd sir tang kich thudc d co' sd. Dieu dd chung td viec pha tap Fe da vao trong mang tinb the. De danh gia mdt each dinh lupng hon sir chuyen pha cau triic tii- tii' giac sang luc giac cua \at lieu chung tdi sir dung chuong trinh profile phan tich ty- le dien tich vach nhieu xa trong viing gdc 26 thay ddi tir 26 ^ 35° va thu dupe ket qua nhu tren bang 1.
Biing I. Ty le giira hai pha cdu tnic Irong vdt lieu khi ndng do pha tgp Fe tdng
X
Tir giac (%) LUC giac
• ( % )
0.00 100 0
0.005 100
0
0.01 100 0
0.02 96.16
3.84 0.03 76.59 23.41 Hinh 2 la phd tan xa Raman ciia tat ca cac mau. Khi x = 0 va pha tap vdi ndng dp rat nhd. mau cd cac vach manh dac trung ciia cau tnic tii' giac d vi tri 180 (peak 1), 260 (peak 2), 305 (peak 3), 519 (peak 4) va 716 cm"' (peak 6). Ket qua nay trimg vdi cac cdng bd
[1.5-8.10.12.]. d dd nguyen nhan eiia cac mode dao ddng da dugc giai thich chi tiet. Cu thi la: Peak 1: d khoang 180 c m ' [E(TO), E(LO)]. Peak 2: d khoang 260 cm"' [A|(TO)].
mode nay do dao ddng eiia bat dien oxy [17]
nen nd r4t nhay vdi ung suat trong mau, khi irng suat tang thi cudng dp dinh nay giam manh [18]. Peak 3: d khoang 305 cm"' [B,, E(T03+L03)]. Peak 4: d khoang 519 cm"' [E(T04), A|(T04)], day la mdt dinh ed cudng dp manh va rdng (mode E(TQ4) dugc coi la mode gian do su thay ddi chieu dai lien ket Ti-0). Peak 6: d khoang 719 em''(E(L04), A,(L04)).
200 400 500 800 1000
Sd sdng (cm" )
Hinh 2. Pho tan xa Raman cua cua cac mau Ba(Ti,.,Fe0O3(0<x<0.03)
Tuy nhien khi pha tap Fe vdi x = 0.01 trd di cac dinh phd dac trung ciia cau triic tir giac yeu di va xuat hien su md rdng vach pho.
Ddng thai vdi sir suy giam cudng dp cua cac dinh tren la su xuat hien them vach tan xa d g4n vi tri 640 cm"' (peak 5). Nguyen nhan xuat hien vach tan xa tai 640 em"' cung da dupe mpt sd tac gia de cap tdi nhung chua thdng nhat [1,7]. Theo Qin-yu Hea va cdng su, khi tdng hpp BaTiOs tir hdn hpp BaO - TiO, vdi nhiet dp thieu kit dudi 1050°C. h?
tdn tai hgp thuc Ba4TiOi3O30 va tren pho Raman xuat hien vach gan 644 cm" . Do do
\ach gan 640 cm"' dugc cho la ddng gdp ciia Ba4TiOi303o- Tuy nhien, theo eac tac gia [12,7] thi dinh gan 640 cm"' la vach dac trung cua BaTi03 cd cau triic luc giac va la mode E(LO). Ket qua phan tich nhieu xa tia X ciia 40
Nguyen Van Dang vd cs Tap chi KHOA HOC & CONG NGHE 78(02): 39 - 44 chiing tdi cho thay cac mau hoan toan sach
pha, do dd vach gan 640 cm"' theo chung tdi chinh la dinh dac trung cho cau tnic lue giac.
Viec xuat hien dinh tan xa gan 640 cm"
[E(LO)] cd the la do tan xa manh tu pha luc giac d nhiet dp cao ciia BaTi03. Day la mdt diem la vi pha luc giac cua BaTi03 thudng chi tdn tai d nhiet dp cao rat cao (tren 1600 C). Tuy nhien su tdn tai eiia pha luc giac trong be mau da dupe khang dinh tren co' sd gian dd nhieu xa tia X. Ket qua thu dugc tren phd tan xa Raman mdt lan niia cung cd them ket luan tir gian dd nhieu xa tia X da thu dugc.
De thu dugc cac ket qua dinh lupng ban, chiing tdi da tien hanh phan tich tirng dinh phd Raman mdt each chi tiet. Ddi vdi tirng phd Raman, chiing tdi su dung phan mem de tach rieng tung dinh, tir do thu dupe: vi tri, ban dp rdng va cudng dp tich phan cua tii-ng dinh phd. Hinh 3 minh hpa phep tach dinh tir mpt dinh phd. Trudc het sd lieu dugc lam khdp theo phuong phap lam khdp nhieu dinh phd. Ham dupe sir dimg de lam khdp la ham Lorentz cd dang nhu sau:
y = yo +
2A w
n 471 (x - XQ)~ + u' Trong dd:
A: cudng dp tich phan ciia dinh.
w: dp rdng d niia cue dai ciia dinh x^: vi tri dinh.
yo: cudng dp phd nen.
Ket qua cho thay vj tri cua dinh 3 d khoang 300 em"' [B,. E(T03+L03)] hki nhu khdng thay ddi. Trong khi cac dinh 4. 5. 6 deu cd xu hudng dich vl vecto sdng nhd ban khi tang nong dp pha tap. Sir dich dinh nay cd the giai thich la do khi Fe dupe dua vao mang tinh the ciia BaTi03 dl thay thi cho Ti. nd se lam gian mang vi ban kinh eiia ion Fe" (0.7 A) Idn hon so vdi ban kinh cOa ion Ti^' (0.6 A). Cang tang ndng dp pha tap se cang lam cho mang bi gian va cac dinh Raman se dich dan ve phia sd sdng nhd hon [16].
OJ Q.
1^
U D.'—' 3
•'<5
• ^ 2
U
0.005 0.01 0.015 0.02 0.025 0 03
Nong do pha tap (x)
Hinh 3. Ty le cudng do giua hai dinh tan xa d vj tri gan 519cm"'va640cm"'
Neu ta xet dinh 4 tuong ung mode E(T04), A1(T04) d khoang 519 cm"' va dinh 5 tuong ling mode E(LO) d khoang 640 cm"' day la 2 dinh cd cudng dp manh nhat va dac trung cho 2 pha tii' giac va luc giac. Tren hinh 3 la dd thi cudng dp ti ddi cua 2 mode nay. Cudng dp ti ddi giam khi tang ndng dp pha tap, dieu nay ddng nghTa vdi ti le pha tii- giac trong mau da giam so vdi pha luc giac. Ta cd the thay ro dieu nay tir su bien ddi cua phd Raman theo ndng dp pha tap. Khi tang ndng dp pha tap, cac dinh dac trung cho pha tu giac giam cudng dp trong khi cac dinh dac trung cho pha luc giac cd cudng dp tang dan. Dac biet vdi ndng dp pha tap nhd (x = 0.005 H- 0.02), cudng dp ti ddi giam manh, ti phan cau triic tii' giac trong mau giam manh, thay the bang cau tnic luc giac. Khi ndng dp pha tap nam trong khoang 0.02 < x < 0.03, cudng dp ti ddi thay ddi it cho thay ti phan pha tii' giac/pha luc giac trong mau thay ddi khdng dang ke.
Theo ket qua phan tich tii' phd nhieu xa tia X thi cau tnic tii- giac giam manh khi 0.02 < x <
0.03 nhung phan tich tir phd raman cho thay pha tii' giac giam manh khi ndng dp pha tap rat nhd x = 0.005 -^ 0.02, hai ket qua nay la hoan toan phu hgp vdi nhau vi phep phan tich raman ed sai sd den 5% trong khi phep phan tich tir gian dd nhieu xa tia X sai sd cd the Idn hon.
Nauven Van Dang va cs Tap chi KHOA HOC & CONG NGHE 78(02): 39 - 44 Hinh 4 trinh bay ket qua do phan thuc ciia
bang sd dien mdi d nhiet dp phdng trong khoang tan sd tir 10 Hz den 13 MHz d trang thai mau chua phan cue. O viing tan sd thap (dudi 500 KHz) hang sd dien mdi eiia tat ca cac mau deu giam dan khi tan sd tang. Viing tan sd cao (tren 1000 KHz), eac mau cd x = 0.00 + 0.02 cd hien tupng cdng hudng dien mdi d trong khoang tan sd tu 600 den 1000 KHz. Khi ndng dp pha tap Fe tang thi hang sd dien mdi ciia vat lieu giam va tinh dan eiia vat lieu tang. Khi ndng dp pha tap tang viing edng hudng cd ve se xay ra d viing tan sd cao.
2.4 10"
1.6 10' 1.2 10' OJ
8000 4000
2000 4000 6000 8000 1 IO"* 1.2 lO"
f(KHz)
Hinh 4. Phan thirc ciia hang sd dien moi phu thugc vao tan so va ndng dg pha tap Fe
Phd hap thu cua cac mau dupe chi ra tren hinh 5. Ket qua cho thay bd hap thu dich ve phia sdng dai va vung hap thu md rdng khi tang ndng dp Fe. Ket qua tinh toan cho thSy be rdng dai cam ciia mau khi chua pha tap Fe (x = 0,0) la 3,23 eV. Bd h4p thu cua mau BaTi03 thu dugc iing vdi su dich chuyen giira trang thai 2p eiia oxy va trang thai 3d ciia titan [14,15]. Bd hap thu dich ve phia sdng dai thi dp rdng vung cam giam. Su giam bl rdng dai cam cd the la do cd su xuat hien cac mire tap chat trong dai cam cua BaTiOs. Fe ddng vai trd nhu tap chat dono va tao nen mue nang lupng tap chat lam cho be rdng dai cam giam. Dieu nay mdt lan nira khang dinh su pha tap Fe da vao mang tinh thi. Cdn sir md rdng vung hap thu cd the la do nhirng hap thu ndi trong cac nguyen tu' tap chat.
42
200 400 600 800 1000 1200
Budc sdng (nm) Hinh 5. Phd hap thu cua he mau Vdi muc dich kiem tra sir ddng tdn tai ciia pha sat tir cimg pha sat dien, dudng tir tre ciia cac mau dugc do trong tir trudng 1 TesIa d nhiet do phdng. Ket qua cho thay trong viing tir trudng thap (dudi 1000 Qe) tat ea eac mau diu thi hien tinh sSt tir. Khi H > 1000 Oe mau cd X = 0.0 the hien tinh nghich tu, cac mau pha tap the hien tinh thuan tir (hinh 4). Theo mdt sd tai lieu [13] vat lieu khdi BaTi03 the hien tinh nghich tir d nhiet dp phdng. O day.
ket qua do tir cho thay mau BaTi03 vira tdn tai tinh nghich tii- va sat tu-. Chiing tdi cho rang ngudn gdc tii- tinh xuat hien trong BaTi03 la do sir khuyet thieu oxy trong mau.
Ve hoa trj ciia sat trong cac mau pha tap la bao nhieu, hien van cdn nhieu tranh cai nen ddng gdp vao tij tinh ciia vat lieu ed the co nhieu nguyen nhan. Nhu tren da ndi, su xuat hien cae mit khuyet oxy anh hudng len tinh chat, dac biet la tinh chat tu cua vat lieu. Hinh nhd eiia hinh 4 la dudng tu' tre ciia mau ed x=
0.0 va 0.005 cho thay dudng tir tre cua mau x
= 0.0 la tdng hgp ciia hai pha sat tii- va nghich tir. Ket qua cho thay, dii pha tap Fe vdi mpt lugng vd cimg be (0.5%) nhung tinh sk tir tang manh chirng td ngudn goc tir tinh xuat hien trong mau phan Idn la do sir khuyet thieu oxy trong mau. Vi neu coi nguon gdc tir tinh ciia cac mau cd chira Fe'* la do tuang tac sieu
Nguyin Van Dang va cs Tap chi KHOA HOC & CONG NGHE 78(02): 39 - 44 trao ddi giira cac ion tir tinh Fe'* thdng qua su
phii nhau vdi ham sdng dien t u ciia ion khdng tir tinh O"" thi vdi h a m lugng Fe thay the nhd nhu vay chua the ddng g d p dang ket vao tinh sat tir ciia mau. M a t khac, khi thay t h i Fe cho Ti do sir khac nhau giira trang thai hoa tri giira Fe va Ti nen de can bang v l hda trj, trong mau phai xuat hien s u khuyet t h i l u oxy.
0.03
x = 0 00
—o X = 0.005 x=0,01 x = 0.02 x=0.03
-1 10' -5000 0 5000 H(Oe)
Hinh 6. Dudng tu tre ciia ciia cac mau do d nhiet do phdng
Chiing tdi da che tao d u g c he mau Ba(Ti|.
xFex)03 (0 < X < 0.03) hoan toan sach pha bang p h u o n g phap phan ung pha ran. Ion F e * da the vao vj tri Ti"** va lam cho vat lieu chuyen pha cau tnic tii' t u giac sang luc giac d ngay nhiet dp phdng. Vach tan xa Raman gan 640 cm"' chinh la dinh dac trung cho cau true luc giac ciia vat lieu. Ket q u a phd hap thu cho thay F e ' * d d n g vai trd n h u tap chat dono lam giam b e rdng dai c a m , giam hang so dien mdi, tang dp dan c u a vat lieu. Phep do d u d n g c o n g tu- hoa c h o thay vat d d n g tdn tai hai pha sat dien va sat tu- d nhiet dp phdng. N g u y e n nhan g a y ra tu- tinh trong vat lieu cd the lien quan tdi s u xuat hien cac niit khuyet oxy t r o n g vat lieu.
L o i c a m c n . Cdng trinh nay d u g c thuc hien vdi sir hd t r p ve kinh phi eiia de tai cap Bd ma S 6 B 2 0 1 0 - T N 0 6 - 0 2 .
TAI LIEU THAM K H A O
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Bendersky, Appl. Phys. Lett. 78, 2536 (2001).
[3]. T. A. Vanderah, J. M. Loezos, and R. S.
Roth, J. Solid State Chem. 121, 38 (1996).
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Lefkowitz, Solid State Commun. 5, 429 (1967) [5]. M. DiDomenico, Jr.S. H. Wemple, S. P. S.
Porto, and R. P. Bauman, Phys. Rev. 174, 522 (1968).
[6]. G. Bums and B.A. Scott, Solid State Commun. 9, 813 (1971).
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Waser, J. Raman Spectrosc. 38, 1288 (2007) [8]. Fangting Lin, Dongmei Jiang. Xueming Ma, Wangzhou Shi, J. Magn.Magn.Mater.320, 691 (2008).
[9]. A. Rajamani, G. F. Dionne, D. Bono, and C.
A. Ross, J. Appl. Phys. 98, 063907 (2005)
[10].E. Mashkina, G. McCammon and F.
Seifertb, J. Solid State Chem. 177, 262 (2004).
[ll].Ning Zhang, Jianjin Wei, J. Magn. Magn.
Mater. 320, 2387"(2008).
[12].Z. Lazarevie, N. RomCevic, M. Vijatovic, Proceedings of the Tenth Annual Conference of the Materials Research Society of Serbia, September 2008.
[13].T.Wolfram, R.Hurst and F.J.Morin, Phys.
/?ev. B 15, 1151 ri977).
[14].Garima Gupta, Tashi Nautiyal, and Sushil Auluck, Physical Review B 69, 052101 (2004).
[15].Manuel Cardona, Physical Review 140, I 133 (1965).
[16].N. K. Karan, R. S. Katiyar, T. Maiti, R. Guob and A. S. Bhallab, Journal of Raman Spectroscopy 40(4). 370 (2009).
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Sawaguchi, J. Phys. Soc. Japan 57 (I), 147(1987).
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Nguyen Van Dang va C5 Tap chi KHOA HOC & CONG NGHE 78(02): 39-44
ABSTRACT
STUDYING THE EFFECT OF SUBSTITUEVG TI'S ATOM FOR FE AND ELECTROMANAGTIC PROPERTIES OF BATIO3
Nguyen Van Dang'*, Nguyen Khac Hung', Ngo Thi Lan', Vu Dinh Lam^ and Le Van Hong"
'College of Sciences - Thai Nguyen Universit\- 'Institute of Material Science - Vietnam Academy of Science and Technology Samples of multiferroic BaTii^FCvOj material (0.0 < x < 0.03) were synthesized by using the solid-state reaction method. The influence of Fe substitution for Ti on the crv'stalline structure and the magnetic property of BaTi^.^FevOj samples were investigated. The obtained X-ray diffraction patterns showed that the stmcture of the material sensitively depends on Fe dopant content, x, and transforms gradualh from the tetragonal phase to the hexagonal one with increasing x. All of the samples exhibit both ferroelectricit\ and ferromagnetism at room temperature. The substitution of Fe into Ti sites also changes the conductivity of the material and impurity (acceptor) levels in the band gap. which can be evident from the absorption spectra, electric impedance...measured at room temperature.
Keywords: BaTi.yFe^O}. XRD. Raman spectra, UV -visible spectra, magnetization, Midllferrolcs
Email: nvdangsptn@yahoo. com 44
