NguySn Thj Dung vd Dtg Tgp chl KHOA HQC & CONG NGHE 162(02): 107-112
TINH CHAT DIEN - TlT vA QUANG HQC CUA VAX LIEU MULTIFERROIC BaTii.^Mn^^Oa TRONG PHA LUC GIAC
Nguyen Thj Dung', Nguyen Viit HoSng^, Nguyin Van D i n g ' 'Trudng Dgi hpc Khoa hoc - DH Thai Nguyen
'Truong Cao ddng suphgm Thai Nguyen T O M T A T
Vat li|u multiferroic BaTii.^Mnx03 (5^0.0;0.07<x < 0.12) (BTMO) dupe cliS tgo b b g phuong phap phan img pha rln. Anh hudng ciia su thay thS Mn cho Ti Ifin clu tnic tinh the, tinh chat dien - Xis va quang hpc ciia vat li?u BaTii.jMnxOs da dupe khao sat chi tiit. Kit qua phan tfch gian do nhieu xa tia X cho thiy, khi Mn thay thi cho Ti, cau true ciia vgt li§u chuyen tii clu true tii giac (P4mm) sang cau tnic luc giac (Pfij/mmc). Tat ca cac mlu pha tap deu d6ng t6n tgi ca tinh chat sSt dien va tinh chit sit tir d nhiet d$ phdng. Kit qua do tir dp phu thupc tir tnicrng ciia cdc mlu cho thiy, tu dp bao hda cua cac mlu tai tir trudng 2 Tesla tang tuyin tinh theo x. Anh hudng cua su thay the Mn cho Ti ISn tinh chit din v i d§ rdng viing d m ciia vat lieu ciing dupe chiing toi khao sat thong qua phep do pho h i p thu
T u k h i a : Vgt lieu multiferroic, XRD. Hdp thu dnh sdng, Tirdo MCi D A U
Mac dii d u g c phat hi?n rat sdm, vat lieu BaTiOj (BTO) voi cac tinh chat dien, tii dgc biet vSn la mgt 6k tai nghien ciht soi n6i tai cac phong thi nghiem tren the gidi cung n h u tai Viet N a m . N h a cau true perovskite dac trung (ABO3), loai vat li?u nay chua d\rng nhiSu tfnh chat ly thii ve tinh sat dien (dien moi, ap di?n...) va da dugrc d u a vao ung diing trong m§t s6 t h i l t bi cua nhieu nganh ky thugt [l]-[5], Gan day, co nhi6u cong trinh nghien ciiu xet toi viec pha tap cac nguyen t6 co tu' tinh n h u Fe, M n , N i , C o . . . v a o vi tri ciia Ti de vat lieu d o n g ton t?i hai phan c\rc dien va phan cg:c tir, nghla la v§t lieu d 6 n g bieu hien ca tinh c h i t sSt tii va s4t dien (vat lipu multiferroics) [2]-[6]. Do vgt lifu multiferroics, co the diing tir trutmg de dieu khiln tinh chat dien cua vgt li?u hoac n g u o c lai, CO t h i dimg di?n truong d l dieu k h i l n tinh chat tir nen n o m a ra kha nang iJng dung to lan trong cac nganh khoa hpc va cong nghe nhu: kha nang thu nho linh kien, tang mgt do linh ki^n, tang t6c dp ho^t dpng va m a ra kha nang c h l tgo cac linh kien to hpp nhieu chuc nang tren cimg mot chip... D o vay, day la mpt h u d n g nghien ciiu hi?n thu hut sy chu y cua cac nha khoa hpc ca trong nghien cihi ly
' Tel. 0983 009975. Email
thuyet va u n g dung trong cac thiet bi hien dgi.
Hi?n nay, co rat nhieu cong trinh nghien cii'u coi BaTiOs la vat lieu nen ly tudng trong ung dyng cac hieu il'ng vgt ly moi bang each pha tgp vao vat lieu d l dieu khien va lam thay d6i cac tinh c h i t ctia chiing. Khi thay t h i mot p h i n Ti bcfi M n , sy bien doi mgnh ve cau triic se lam cho tinh c h i t ciia vat lieu thay d6i. V i n de dgt ra la phai t?o ra d u a c vat lieu co cau tr6c on djnh va dong ton tai tinh chat sat di^n va s i t tir cf nhipt dp phong.
Trong bai bao nay, chiing toi trinh bay mpt so k i t qua nghien ciiu ve tinh chat dien - til' va quang hoc cua vat lieu multiferroic BaTij.
,Mn«03 (x= 0.0; 0,07 <x < 0.12) trong pha luc giac a nhiet dp phong,
T H U C N G H I E M
Cac m l u da tinh t h i BaTii.,Mn,03 (x = 0.0;
0,07 < X < 0.12) dupe che tao b i n g p h u a n g phap phan irng pha ran. Cac hoa chat ban dau la: MnOa, BaCOs, Ti02 voi do sach tren 99,99% sau khi can theo dung h a p thiic danh dinh dug'c nghien trpn bang coi ma nao, ep vien va nung sa bO 6 nhi?t dp lOSO^C trong 24 gia. San p h i m sau do d u p e nghiln trpn va ep vien lin hai va nung thieu ket a nhi?t dp nOO^C trong thai gian 5 gia. D o sach pha va cau tnic tinh the ciia cac mau d u p e kiem tra b i n g p h u a n g phap nhieu xa tia X tren nhieu 107
Nguyin Thi Dung vd Dig Tap chi KHOA HOC & CONG NGH$ 162(02): 107 - J xa kl SIEMENS D5000 vai biic xa CuK^ {% =
1,5406 A). Anh SEM ciia mlu dl khao sat kich thuoc hat dupe thyc hi^n tren kinh hiln vi di?n tit quet FE-SEM S-4800 ciia hang Hitachi. Phep do tinh chat sit dien dupe thyc hien tren he do Model LClOV cua hang Radian Technologies- My. Phep do tii dupe thyc hien tren he do cac tinh chat vat ly PPMS 6000 tai Vi?n KHVL - Vien Han lam KH & CN Viet Nam. Phep do ph6 hap thy trong viing buoc song tir 200 -^ 1200 nm dupe thuc hien tren he do JACO V-670 tgi Khoa Vat ly, Tnrang Dgi hpc Su phgm Ha Npi.
KET QUA VA T H A O LUAN
Hinh 1 la kit qua do gian do nhieu xg tia X (XRD) ciia cac mau trong khoang goc 2^ tii 20° den 80°, vai buac quet 0,02°. Ket qua cho thay, cac dinh pho co cucmg dp manh va rat
sic net chtj'ng to cac mau hoan toan sgch pha, ket tinh tot va it sai hong. Khi chua pha tap (x=0.0) vat lieu BaTiOs co cau tnic tii giac thupc nhom khong gian P4mm, gian do XRD CO dinh a vj tri goc 29 = 31.5° c6 cudng &^
lan nhat so vai cac vi tri khac. Khi thay the Mn cho Ti v6i nfing dp 0,07 <.\<. 0.12, gian dl XRD cho thay vat lieu co cau tr6c perovskite va phii hpp vai pha tinh thi luc giac vol nhom doi xung khong gian P63/mmc. Doi chieu voi the chuan cua BaTiOj ling vdi cau tnic luc giac ta tim dugc cac dinh tuang ung vai su phan xg cua chiim tia X tren cac ho mat phing nhu dugc chi ra tien hinh 1. Pho XRD ctia cac mau pha tap trong khoang 0.07 < x :£ 0.12 thay doi rat it chiing to pha cau tnic ciia vat lieu gan nhu on dinh va co the coi la don pha cau tnic luc giac.
Tii: giac Luc giac
50 G6c 2^(48)
Hinhl. Gidn 36 nhiiu xa tia X ciia he mdu Ba(Tii.^Mn,)03 fx^O. 0; 0.07< x<0.12}
De CO them cac thong tin ve kich thiroc hat cung nhtt xu hltong phat trita cua kich thuac hat klii Mn thay the mpt phan cho Ti, mpt so mau dai dien da ditpc mang di chup anh SEM nhir to(tc trinh bay tren hlnh 2. Ket qua cho dijy mlu BTO (x=0.0) c6 mat dp hst kha ddng dSu, bien hat ro va sac net, ca hat phat triln kha Ion voi kich thir6c hat trung binh khoang tit 1,5 dSn 2 (tm. B}t biet, dp xep chat ciia mlu khong cao va nhiSu 16 h6ng, di6u nay goi y rang dien tra va hSng so dien moi ciia vat li^u BTO o nhiet dp phong se kha cao.
108
NguySn Thi Dung va Dtg Tap chi KHOA HOC & C 6 N 0 NGHE 162(02)- 107-112
^ t
(c)
Hinh 2. Anh SEM cua mgt sd mdu dgi dien cua he Cac ket qua tren hinh 2 (b,c,d) cho thiy, khi nong dp Mn thay the cho Ti tang mgt dg hat va do xep chat cung tang, bien hat hinh thanh rit ro va cac hat tiep xuc vai nhau rat kbit.
Dac biet, kich thuac hat trung binh ciia mlu tang tir khoang 1.5 pm (x = 0.0) dSn khoang 4
|im (x = 0.12). Theo [I] thi kich thuac hat ciia vat li?u BTMO co anh hu6ng mgnh toi hang so dien moi cr tin so thap, hang s6 dien moi tang len khi kich thuac hgt giam. Nhiing ket qua nay cho phep chiing ta dua ra nhan dinh rang khi 0.7 < x < 0.12 di?n tra a nhiet dp phong ctia cac mau BTMO se giam khi nong dp X tang. Qui lugt nay ciing phu hgp v6i ket qua cua nhieu cong trinh da cong bo [3]-[7].
Cac ket qua do duong tre sat di^n ciia mot so mau dgi dien ciia he mau BTMO dupe trinh bay tren hinh 3. Ket qua cho thay, mau BTO va cac miu pha tap dai di^n cho he mau BTMO (v&i 0.07 < X < 0.12) deu thu dugc duang cong dien tre dac trung ciia v^t lieu sat dien a nhiet dp phong. Tir d?ng duang tre tuang ung vai gia tri di^n ap giii'a hai cue ciia mau la 300V, chiing ta chua the danh gia va xac dinh chinh xac sy thay doi cua dp phan eye eye d^i (Pmax), dp phan eye du {Pr) va truang di?n khang (Ec) ciia cac mlu. Tuy nhien, neu so sanh vai mau BTO ta thay, cac mau pha t^p co gia tri Pmax tai di?n truang do CO xu huang giam nhung trucmg dien khang {Ec) cua cac mau co xu hiiong tang len, cac mlu pha t9p van ton tgi dac tnmg sat dien
(d)
BTMO (x^O.O (a);x^0.07 (b); x=0.I(c); x=0.I2(d)) manh tuong duong vdi mau BTO. Ket qua nay cOng phii hgp vai mpt so ket qua dupe cong bo gan day khi cho rang: khi Mn thay the cho Ti da thiic day manh me sy hinh thanh cua pha luc giac co Ipi cho tinh sat dien [i].
Hinh 4 la ket qua do duong cong tur tre M(H) ciia he mau, hinh nho ben trong hinh 4 bieu dien ket qua do ciia mau BTO khi chua pha tgp. Ket qua cho thay, khi chua pha tap mau X = 0,0 the hien tinh nghjch tii va co tinh sat tii rat yeu d viing tii trudng thap. Khi pha tgp Mn, tir do bao hoa ciia mau tang gan nhu tuyen tinh voi nong dO tgp chat. Tuy tir dO bSo hoa tang tuyen tinh theo x, nhung theo kit qua phan tich nhieu xg tia X cho thay cac mau che tgo la sach pha nen co the khang dinh tir d$ ciia mau la do ban chat ngi tai trong mau quyet dinh, dong gop vao tir tinh cua cac pha thii cap nhu cac dam Mn, Mn02, Mn204.,, dupe loai trir. Dac biet, trong pha luc giac (vcri 0.07 < x < 0.12) thi cac mau deu the hien tinh sat tir a nhiet dp phong.
De giai thich tinh chat tir cua vat lieu DMS vdi tgp chat Mn, nhieu nghien ciru thuang dya tren hai logi tuong tac la tuang tac trao doi kep va tuong tac quy dgo p-d. Tuy nhien, theo [7] vdi dien trd suat rat cao nhu vat li?u BTMO, kha nang ton tai tuong tac trao doi kep va tuong tac p-d la rat nho. Theo [9]-[i I], CO thi dua vao mo hinh polaron tir lien kit (bound magnetic polarons-BMP) dupe dl xuat bai Coey va cpng sy [10] de giai thich
109
Nguyin Thj Dung vd Dtg Tgp chi KHOA HOC & CONG NGHb iDzi,uzj: iu/ - m.~
cac dac trung tir tinh thu dugc tren he BTMO.
Theo do, tinh sat tii cua vgt lieu B T M O co the CO lien quan den sy hinh thanh cac polarons tir lien k i t tao bdi cac dien tit lan cgn (co nguyen nhan tii sy khuylt thieu oxi trong mau) va ion Mn''*. Theo chiing toi, tinh chat tir ciia vat lieu B T M O khi 0.07 < x £ 0,12 co nhieu nguyen nhan. Thii nhat la sy dong gop vao tir tinh cua cac mit khuyet trung gian co nguyen nhan tir su khuyet thilu oxi trong mau. Ngoai ra, tii tinh ciia vat lieu B T M O cung phu thupc vao vi tri ciia cac ion Mn, su thay doi hoa trj va hieu ling meo mang Jan- Tellerr trong vat lieu. Ngoai sy b i l n d6i ctia t;y le ion cua Mn^* va Mn^* trong mau theo nong dp thay the x, vj tri ciia cac ion M n thay the vao vi tri cua Ti cung dong vai tro quan trong vao tii tinh ciia vat lieu. Theo [1],[8], trong cau tnic luc giac, cac ion Mn cd the chiem cac vi tri ciia Ti (1) va Ti (2) va luong tac giira cac ion Mn d hai vj tri nay se quyet dinh tinh chat tuciia pha luc giac. Do
khoang each (hay dp dai lifin k i t ) tu Ti (1) den O (1) Idn b a n khoang each tit Ti (2) den O (2) rat nhieu [9], nen tuong tac trao d6i giira cac ion Mn tai cac vj tn'Ti (1) vaTi (2) ciing n h u tuong tac trao doi tryc tiep gifta cac ion Mn tgi cac vj tri Ti ( I ) vdi nhau la rat yeu. Ket qua la, sy thay the cac ion Mn vaov[
tri Ti (1) chi ddng gdp vao tinh chat thuan fi- chi CO tuong tac giira cac ion Mn tai c^c vi tri Ti (2) vdi nhau la cd the ddng gdp dang k£
vao tinh chat sat tir ciia vgt li?u.
Hinh 5 trinh bay ket qua do pho hap thu ciia cac mau. Chiing ta de dang nhan thiy bd hap thy ciia mau BTO tai budc sdng khoang 38S nm, do do dp rpng viing cam ciia mau BTO co the dupe xac dinh gan diing theo cong thiic:
^ he 6,625.I0"^.3.10° 1242,19 „ , , -^^
^'=T=" 1 »l^-^''<"'>«
trong dd X la budc song hap thu. Kit qua nay phii hop vdi cac cong bo ve do rgng viing elm ciia B T O .
0 1 5 0 1 0 05
-0.05 -0 1 -0,15
-0.2
100V 200V 300 V
r, , , ,
^^r .
^^^
x = 0.0 \ (a) \
'.
-300-200-100 0 100 200
Dien the sii dung (V) Hinh 3. Ducmg tre sdl dien cua mot
- 3 0 0 - 2 0 0 - 1 0 0 0 100 200 300
Dien the su dung (V) sd mdu dai dien cho he BTMONguyen Thj Dung vet Dtg Tap chi KHOA HOC & CONG NGHE 162(02). 107 - 112
-2 -15 -1 -0.5 0 05 1 1.5 2 H(kOe)
Hinh 4. Ehtang cong tit tri ciia cdc mdu Ba(Ti,.
MnJOsfvaiO.O, 007£x£0.12}doanhietdophong
OS
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•£ 04
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^ „ , .
^ • ^ ^ S . \ ^ x = 009 1 ^^SN^Vk — r-)(:0.0
300 40O 500 600 700 800 900 1000
Hinh 5. Pho hdp thu da he mdu BaTii.,Mnx03 (x=0.0; 0,07 <x <0.12) do a nhiet do phong Pho hap thu cho thay bd hap thy ciia cac mSu pha tgp md rgng va djch ve phia budc song dai khi nong dp Mn thay th6 cho Ti tang.
Dieu nay cd the la do dong gop cua cac tr^ng thai tgp Mn gay ra. Day ciing la mgt bSng chiing thyc nghiem dang tin cay chung td Mn da di vao cau true, thay the cho Ti h-ong vgt li?u BTO. Cac trgng thai tgp trong viing cam ciia vat li?u BTMO dupe hinh thanh tren co sd cac miic nang lugng cua cac dien tii 3d cua cac ion Mn va cac khuyet tgt mgng tinh the.
Tir do thj cho thay c6 ve nhu ba hap thy ciia vat li?u giam khi x tang. Tuy nhien, khi x tang cao rSt khd cd the xac djnh chinh xac bd hap thy. Khi ndng dp pha tap tang, vimg hip thy
gan nhu md rpng trong toan dai budc sdng do. Tiic la cac mau co kha nang hap thy toan bg anh sang trong vung kha kien va mgt phan trong vung anh sang hong ngoai. Sy md rgng bd hap thu nay cd the lien quan tdi ddng gdp ciia cac qua trinh chuyen ddi giiJa cac trgng thai nang lupng ctia ion tap va chuyen ddi inirc tap len viing dan cua vat lieu. Ket qua nay cd the lien quan den mii'c nang luong dien tii 3d ciia ion Mn*"^ tren trang thai TJQ (mii'c Eg trong), KET LUAN
Bang phuong phap phan ling pha rSn, chiing toi da che tao thanh cong vat li?u BaTi|.
xMn.Os (vdi x= 0.0; 0.07 < x < 0.12) hoan toan sach pha va diing hpp thiic danh dinh.
Ket qua phan tich gian do nhieu xa tia X cho thSy he chuyen tir cau tnic tu giac sang cau true luc giac khi Mn thay the cho Ti trong mgng tinh the. Ket qua khao sat tinh chat dien tir ciia vat lieu cho thay, tat ca cac mau pha tap deu the hi?n sy dong ton tai tinh chat sSt di$n va sat tir d nhiet dp phong. Trong khoang pha tap (0.07 < x < 0.12) cac mau cd tir dg Idn va tang tuyen tinh theo nong dp Mn thay the cho Ti. Phep do pho hap thy cho thay cac ion Mn da thay the cho Ti trong cau tnic cua vat lieu BTO. Sy xuat hien cua cac mu'c tap chat Mn ket hgp vdi cac muc tgp do sy khuyet thieu oxy, sai hong mang... tao nen su chdng cheo, md rpng ciia cac dai hap thii va lam djch bd hap thy ve phia sdng dai, LC31
C A M O NNghien ciiu nay dugc tai trg bdi Quy Phat trien khoa hpc va cdng nghe Quoc gia (NAFOSTED) trong de tai mS so 103,02-2015,56 vade tai Khoa hpc va Cong n ^ e cap Dgi hpc Thai Nguyen ma s6 DH2014-TN07-06.
TAI LIEU THAM KHAO 1. N. V. Dang, The-Long Phan, T. D. Thanh, V.
D, Lam, and L. V. Hong, (2012), "Structural phase separation and optical and magnetic properties of BaTi|.,Mnx03 multiferroics", J. Appl Phys. ill, 113913,
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t i l
Nguyen Thi Dung va Org Tgp chi KHOA HOC & CONG N U H t ioz(.ozj; lui-tm 3. K.F. Wang, J.M. Liu and Z,F. Ren (2009),
"Multifenoicity: the coupling between magnetic and polarization orders", Advances in Physics 58, pp. 321-448.
4. R. Maier and J. L Cohn (2002), "Ferroelectric and ferrimagnetic iron-doped thin-film BaTiOji Influence of iron on physical properties", J. Appl.
Phys. 92, pp, 5429-8.
5. Yao Shuai, Shengqiang Zhou, Danilo BUrger, Helfried Reuther, Ilona Skorupa, Vamn John, Manfred Helm, and Heidemarie Schmidt (2011),
"Decisive role of oxygen vacancy in ferroelectric versus ferromagnetic Mn-doped BaTiOj thin films", J Appl Phys. 109, pp. 084105-084113.
6. M. Yamaguchi, K. Inoue, T. Yagi, Y.
Akishige (1995), "Soft Acoustic Mode in the Ferroelectric Phase Transition of Hexagonal Barium Titanate", Phys. Rev. Lett. 74, pp. 2126- 2129.
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in highly orientated Mn-doped BaTiOs thin films"
Appl Phys. Lett. 95, 033105-3.
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"Effective interaction Hamiltonian of polaron pairs in diluted magnetic semiconductors", Phys.
flev. S65,pp.075211-8.
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N. T. Dang, D. P. Kozlenko, T. L, Phan, S, E, Kichanov, N. V. Dang, T. D. Thanh, L, H. Khiem, S. H. Jabarov, T. A. Tran, D. B, Vo, B. N, Savenko (2016), "Structural Polymorphism of Mn-Doped BaTlOj", Journal of Electronic Materials 45 (5), pp 2477-2483.
SUMMARY
E L E C T R O M A G N E T I C A N D O P T I C A L P R O P E R T I E S O F BaTii-xMn^Oj M U L T I F E R R O I C S IN H E X A G O N A L P H A S E
Nguyen Thj Dung', Nguyen Viet Hoang', Nguyen Van Dang'' 'College of Sciences - TNU 'Thai Nguyen Pedagogical College ' Multiferroic BaTiL^Mn^Os (x=0.(^0.07<x<0,12) materials were synthesized by the solid-state reaction method. The influence of Mn substitution for Ti on the crystalline structure and the electromagnetic and optical property of BaTi|.,Mnx03 samples were investigated, The obtained X- ray diffraction patterns showed that the stmcture of the material sensitively depended on Mn dopant content, x, and transformed gradually from the tetragonal (P4mm) phase to the hexagonal (Pdj/mmc). Ail of the samples exhibit both ferroelectricity and ferromagnetism at room temperature. The resuh of magnetization measurements showed that the saturation magnetization at a magnetic field as high as 2 T linear depended on x. The substitution of Mn 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 measured at room temperature,
Keywords: Multiferroics, XRD, UV-visible spectra, magnetization
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