DSpace at VNU: Tính chất dị hướng của hệ vật liệu (BI, SB)2TE3+

TINH CHAT D! HUONG CUA HE VAT LIEU (BL SB)2TE3^
NGOTHU HUONG,
Khoa Vat ly - Dai hoc KHTN - DHQG HN
G. NAKAMOTO, M. KURISU
Vien KHKT tien tien Nhgt Ban JAIST
Abstract: The single crystals of Bi, xSb„2Te3+5 {S = 0.0 - 0.90)
compounds were prepared by a Bridgman method from Te rich liquyd.
The anisotropic properties of these compounds were studied. The
Seebeck coefficient is reasonably isotropic for all the samples along
the a- and c-axes. The resistivity is smaller along the o-axis than the
c-axis. In the samples with S> 0.10, their anisotropy ratio of 4 / 4
reaches 2 - 4 . The carrier concentration n is larger for the n-type
samples than the p-type with S=0 and 0.05.
1. Phan md dau

Bismiit Telua la he vat lieu ban dan c6 cau triic Idp va c6 linh di
hxtdng rat manh. O vat lieu don tinh the, tinh di hirdng cua he so
Seebeck, dien trd suat, hang so Hall va do dSn nhiet bieu hien rat ro
rang. Su sai khac thanh phan so vai hgp thiic ban dau trong he vat
lieu nay dugc giai thich la do ton tai nhirng vacanxy hoac 96 sai hong
mang [1, 2]. Vat lieu dir Bi thudng la ban din loai p, vat lieu dir Te
thudng la ban dan loai n.
Trong bao cao nay, chiing toi trinh bay ket qua nghien cxhi tinh chSft
ca'u true va tinh di hu6ng cua he vat lieu Bi, j,Sbo2Te3+s vai 0,0 < 5< 0,9.
2. Thirc nghiem

Dan tinh the Bi, 8Sb„2Te3+5 dugc che tao tir he vat lieu du Te v6i
S=0,0- 0,90. Cac loai vat lieu ban dau Bi, Sb va Te cd do sach 99,99
878

% da dugc sir dung. Cac dan tinh the Bi, sSbojTe^+s dugc nuoi bang
phUdng phap Bridgman vdi gradient nhiet do la 25 K/cm vdi toe do
nuoi don tinh the la 40 mm/gicf.
Cac mlu diing de do he so Seebeck (a), do dan dien va hang so
Hall (RH) la hinh hop c6 kich thudc 3 x 3 x 20 mm"* dugc cat theo hai
true a va c. Cac tham so ve ca'u triic ciia cac thoi tinh the nay dugc xac
djnh nh5 nhiSu xa tia X. Su phu thugc cua he so Seebeck vao nhiet do
a (T) dugc do trong dai nhiet do tir 4,2 K den 300 K. Dien tra suat phu
thuoc nhiet do p (T) dugc do bang phuang phap bon mui do trong dai
nhiet tit 5 K den 300 K. Hang so Hall phu thugc vao nhiet do /?„ (T)
dugc do a t\x trucfng 0,8 Tesla trong dai nhiet tir 77 K den 300 K.
3. Ket qua va thao luan

Vdi m6i mot mSu, phep do phd nh'itu xa tia X (XRD) deu dugc
xac dinh tai ba vi tri tren thoi don tinh the (vi tri dau tren, vi tri giila va
vi tri cuoi). Pho nhiSu xa tia X a tat ca ba vi tri deu chi ra rang khong
CO pha la nao ngoai pha ciia luc giac Bi, j,Sb„2Te3o. Hinh 1 chi ra pho
nhilu xa tia X ciia cac mSu bgt Bi, gSbojTe^+s a vi tri giiia ciia cac dan
tinh the. Tuy nhien, a vi tri dau tren cua cac mSu S = 0,50 va 0,90 c6
th6m mgt vai dinh tai gia tri goc 29 = 23" and 38", nhirng dinh nay c6
the la nhiing dinh ciia Te kim loai. Dieu do c6 nghla la lugng Te du
trong thanh phan tao mau ban dau khong di vao trong hgp phan hoan
toan ma chung tach ra va tap trung d phan dau tren cua thoi tinh the.
8001

1—

1—\
1
r^'l.8^'^0.2TS3+5

— I
I

700

f

5 = 0.50

-K-rK. X

600

8 = 0.90

A »A A-

6 = 0.30

X-^JL

5 = 0.20

300

-A_«A_

5 = 0.15

200

-JL^.A_A^

5 = 0.10

500

•e 400

5 = 0.05

•*A__A<_

100

= 0.0
^

20

- '

40

^ 1

20 60

80

100

Hinh 1: Pho nhiiu xa tia Xciia cac mau bgt BiifjSbojTej^^
879


Hang so' mang o va c ciia he vat ntu u^y ^^v- •--- .
>
phan tich Rietveld. Cac gia tri hang so mang la khong thay d6i chiing
to rang hang so mang khong phu thugc vao nong do Te du dua vao.
Hinh 2a va hinh 2b dua ra su phu thugc nhiet do ciia he so
Seebeck ciia he Bi, xSbojTcj+s theo true a va true c tuang ling. V6i
tat ca cac miu trir mSu c6 J = 0,10 dgc theo true r, gia tri ciia he so
Seebeck la tang khi nhiet do tang. He so' Seebeck c6 tinh di hudng
nhung khong manh. Phat hien nay ciia chiing toi khong he mau
thuan vai ket qua dugc dua ra trong bao cao ciia Goldsmith va cac
cgng su [3].
1

>

'

1

'

BiigSbosTejo+Tes (4N)
a-axis

• 6 = 000
o 0 05
i
010
V 030
-» 050
o 0,90

• 6=0,0
« 0,05
"
0.10
V 030
_»
050
o 0,90

>

^^g,g^^^°-

3.

Bi,eSbo2Te3o+Tes (4N)
c-axis
ODO

a '•
0)

<«aaaas^

s^m^

^^Wi^Bpa>«w»«—_
'

V „
^

o
V -

5J-200
in

1

,

1

.
I

0

100

200

300

Temperature (K)

-0

,00

.

I

.

200

300

Temperature (K)

Hinh 2a: Su phu thugc nhiet do
j^inh 2b: Su phu thugc nhiet
cua he so Seebeck cua he vat lieu ^16 cua he so Seebeck cua he va
BirsSboJcja

dgc theo true a.

/,-^„ Bij^boJe^^s

dgc theo true c.

Hinh 3a va 3b chi ra sir phu thugc nhiet do cua dien tra suat ciia
he Bi, jjSbo2Te3+5 dgc theo true a va true c tuang ling. Tat ca cac k^t
qua deu cho tha'y cac mlu c6 tinh din kim loai trir mSu c6 S= 0,05 ma
a do CO su di thudng. Gia tri dien tra suat Idn nha't thu dugc d nhiet do
150 K ciia mau c6 gia tri S= 0,05. No chi ra rang dien tra sua't c6 tinh
di huang. Gia tri ciia dien tra suat dgc theo true a nho han nhieu so
v6i gia tri ciia dien tra suat dgc theo true c. O nhiing mSu c6 (5 > 0,10,
ty so' di huang ciia S^ / <5, quang tir 2 den 4.

880


0 6 = 0,05
i
010

100

200

Bi,8Sbo2Te3o+Te„ (4N)
c-axis

300

Nhiet do (K)
Nhiet dp (K)

Hinh 3b: Su phu thugc nhiet
Hinh 3a: Si^ phu thugc nhiet do
do cua he so Seebeck cua he
cua he so Seebeck ciia he
Bi, fiSb,y2Tej+sdoc theo true c.
BiijiSbiy2Te}+sdgc theo tnic a.
Hang so Hall RH dugc dua ra tren hinh 4a. Ket qua nay chi ra rang
hkg so Hall la di hudng vdri tat ca cac mlu trii mlu c6 5 = 0,05 and
0,10. Ty so ciia (83,2/ 5,23) = 2,4 khi 5 = 0,0 da dugc so sanh vai ket
qua cua Drabble [4]. Su thay doi ciia he so Hall a 300 K vdi cac thanh
phSn Te du khac nhau cho biet vat lieu chuyen tir ban din loai p sang
ban dan loai n khi 5 nho han 0,1 la phii hgp vai vai ket qua cua phep
do he so Seebeck. Nong do hat tai n ciia he nay dugc dua ra tren hinh
4b. 0 300 K, nong do hat tai n ciia vat lieu loai n la Idn han so vdi
nong do hat tai cua vat lieu loai p khi 5 = 0 va 0,05. Ket qua nay chi ra
rang c6 su thay doi nhiet khac nhau ciia nong do hat tai giiia cac mau
thuoc ban dan loai n va loai p. Gia tri nong do hat tai n a nhiet do 77 K
dat gia tri 16n han khi a nhiet do 300 K. Su phu thugc nhiet do cua he
so cong sua't da dugc tinh dua vao gia tri he so Seebeck va dien trd
sua't. He so cong sua't dgc theo true a Idn han he so' cong suat dgc theo
true c a ta't ca cac mSu.

881


1

E
o

Bi, 8Sbo2Te3o+Te5 (4N)
•

300 K
i

\

\ \

77 K
M H//C, l//a -

« H//a, l//a

c

coneentration

o

";«

^

<.


^

O
., 1
0,1

I

.

02

I

.

0,3

Excess Te content

04

0,1

02

0,3

04

Excess Te content

Hinh 4a: Hang so Hall phu
Hinh 4b: Nong do phan tu
thugc nong do Te du cua he vat lieu ^^'' P^'^ ^/"'(^"^ f^ong do Te du cm
BiigSboyTcj^s

'^^ ^^^ ^'^^ BiiffSbfyyTe^^s

4. Ket luan

Tinh chat nhiet dien ciia he vat lieu Bi|nSb,)2Te3+^ cd tinh di hudng
ra't ro rang. O day, chiing toi ap dung mo hinh six-valley de giai thich,
ma d md hinh nay cung da dugc ap dung trong tinh toan viing hoa tri
cua vat lieu Bi2Te3.
Ldi cam dn

Cac tac gia chan thanh cam an Vien Khoa hoc va Ky thuat tien
tien ciia Nhat Ban (JASIT) da giiip da ve tai chinh de hoan thanh cac
phep do trong bao cao nay.
Tai lieu tham khao

[1]
[2]
[3]
[4]

882

R. F. Brebrick, J. Phys. Chem. Solids 30 (1969) 719.
M. H. Francombe, Br. J. Phys. 9 (1968) 415.

H. J. Goldsmid, Proc. Phys. Soc. Lond., 71, (1958) 633.
J. R. Drabble, Proc. Phys. Soc. Lond., 72, (1958) 380.