r] X ì r$ 3 l , Å Ò & ³p â , M¨ ossbauer ì rF g l x 9 1 l x+ þ Ar « Ñ oÖ ¦8 £ ¤& ñ l \ ¦ s 6 x # ½ ¨ % i

(1)

α-LiFeO

2

ì r ´ ú ` ¦ a % ¦ 0 qZ O ` ¦ s 6 x # ] j ¸ % i . & ñ < Æ& h x 9 l & h $ í | 9 ` ¦ \ P ì r$ 3 © u , x-

r] X ì r$ 3 l , Å Ò & ³p â , M¨ ossbauer ì rF g l x 9 1 l x+ þ Ar « Ñ oÖ ¦8 £ ¤& ñ l \ ¦ s 6 x # ½ ¨ % i

. α-LiFeO

2

é ß { 9 © É r 600

^◦

C \ " f 3r ç ß 1 l x î ß / B N l × æ \ " f \ P % o # % 3 ` ¦ Ã º e % 3 Ü ¼ 9, x- r ] X

ì r$ 3 õ α-LiFeO

2

ì r ´ ú É r cubic ½ ¨ ¸\ ¦ & Ü ¼ 9 s M : © Ã º a = 4.1610 ± 0.0005 ˚ A s % 3

. M¨ossbauer Û ¼& 7 à Ô! 3 ì r$ 3 õ α-LiFeO

²

_ Curie : r ¸ H 90 ± 3 Ke ` ¦ · ú Ã º e % 3 . © : r \ " f α-LiFeO

2

_ s $ í | 9 ^ s 1 l x ° ú כ É r 0.24 mm/s ° ú כ` ¦ & Ü ¼ 9, s H α-LiFeO

2

_ Fe s : r s t H s : r

H Fe

³⁺

_ high spin © I e ` ¦ Ð# Å Ò% 3 . α-LiFeO

2

_ ¨ î ç H íp [ j l © H

hf

(T ) H T /T

C

<0.7

% ò

% i \ " f [H

^hf

(T ) − H

hf

(0)]/H

hf

(0) = −0.36(T /T

C

)

^3/2

− 0.27(T /T

C

)

^5/2

Ð spin wave & ñ ? /\

"

f ¸ ú # l H d` ¦ · ú Ã º e % 3 .

PACS numbers: 74.25.Ha, 75.50.Gg, 76.80.+y Keywords: M¨ ossbauer Û ¼& 7 à Ô! 3 , a % ¦ 0 q ] j ¸Z O , LiFeO

2

I. " e Â ] Ø

o

½ ¢ § s : r t H \ -t x 9 ¸ Z } ¦ l ~ ½ Ó Ö ¦ s ± ú Ü

¼ 9 1 l x{ 9 ^ & h , Á º> { © 6 x | ¾ Ós H © & h ` ¦ t ¦ e .

÷

r ë ß m , B j ¸o ´ òõ \ O # Q" f 6 x © ¼ # o ¦ Ã º

"

î s U ´ . ¸à Ô· ¡ ¤, Ö r ï 8, Ê ë@ / o 1 p x þ j H ] j¾ ¡ § _ è + þ

A o\ t ^ ] j¾ ¡ § \ p u H % ò ¾ Ós & & Ü ¼ 9, Õ ª\ Â Ò¾ ¡ § _ â | ¾ Ó oü < $ èq § 4 oü < 8Ô ¦

#

Q t _ è+ þ A oü < é ß 0 A & h { © @ /6 x | ¾ Ó o ´ ú § É r ' a d s

÷ & ¦ e [1,2]. : £ ¤ y , o ½ ¢ § (Li) õ ^ o = (Fe) í ß oÓ ü t LiFeO

₂

ü < LiFe

5

O

₈

\ @ /ô Ç ½ ¨ H o ½ ¢ § s : r t _ cath- ode Ó ü t| 9 Ð_ 6 £ x6 x õ Å (garnet : Y

3

Fe

5

O

12

)` ¦ @ /

#

Ð $ § 4 ô Ç _ s ß ¼ Ð 6 £ x6 x Â Ò¾ ¡ § > hµ 1 Ï Ð

# ´ ú § É r ½ ¨ s À Ò# Qt ¦ e [3,4]. LiFeO

²

H ½ + Ë$ í

¸| x 9 ~ ½ ÓZ O \ α-LiFeO

2

, β-LiFeO

₂

, x 9 γ-LiFeO

₂

_ 3 t & ñ ½ ¨ ¸\ ¦ t ¦ e . α-LiFeO

²

H d { 9 ~ ½ Ó

&

ñ (fcc cubic) ½ ¨ ¸ Ð, Li

⁺

ü < Fe

³⁺

s : r É r Ô ¦ ½ ©g Ë :& h Ü ¼ Ð

∗

E-mail: [email protected] Tel: 02-910-4752, Fax: 02-910-5170

¼

1 Ï ^ o \ ¦ & h Ä » ¦ e Ü ¼ 9, / B N ç ß ç H É r F m3m s .

γ-LiFeO

₂

(tetragonal, I41/amd) H Li

⁺

ü < Fe

³⁺

s : r s ¼ 1 Ï

^ ½ ¨ ¸\ " f ½ ©g Ë :& h | 9 " f\ ¦ f Ü ¼ Ð & ñ @ / g A$ í s × ¦ # Q[ þ t # Q { 9 ~ ½ Ó& ñ ½ ¨ ¸\ " f ~ ½ Ó& ñ ½ ¨ ¸ Ð

" f % 3 # Q . ¢ ¸ô Ç, β-LiFeO

2

(monoclinic, C2c) H α- LiFeO

2

\ " f γ-LiFeO

²

Ð H × æ ç ß õ & ñ \ " f + þ A$ í ) a [5]. LiFeO

2

Ó ü t| 9 _ l & h : £ ¤$ í É r ´ ú § É r ½ ¨ s À Ò# Qt

¦ e Ü ¼ l & h $ í | 9 \ ' a ô Ç ½ ¨ H ´ ú §s Â Ò7 á ¤ ô Ç z ´& ñ s

. s \ : r ½ ¨\ " f H a % ¦ 0 q ] j ¸Z O Ü ¼ Ð LiFeO

2

\ ¦ ] j

¸ # DTA/TGA, x- r] X l , Å Ò & ³p â (SEM)

`

¦ s 6 x # \ P % o ¸| , & ñ ½ ¨ ¸ x 9 { 9 _ ß ¼l \ ¦ ¸

% i Ü ¼ 9, M¨ossbauer ì rF g l , 1 l x r « Ñ oÖ ¦8 £ ¤& ñ l

\

¦ : x # Li

⁺

, Fe

³⁺

s : r[ þ t _ site ì r í ¸ x 9 l & h $ í

| 9

` ¦ ¸ % i .

II. ÷ m Ç] M ö U ê s0 n É

a

% ¦ 0 q ] j ¸Z O Ü ¼ Ð LiFeO

²

ì r ´ ú ` ¦ ½ + Ë$ í l 0 Aô Ç Ø ¦ µ 1 Ï

"

é

¶ « Ñ Ð" f H í H ¸ 99.99 %_ iron nitrate (Fe(NO

3

)

3

-527-

(2)

Fig. 1. TGA/DTA curves of LiFeO

₂

gel powder.

·9H

₂

O) x 9 99.99 %_ lithium acetate (CH

3

CO

₂

Li)\ ¦ 6

x % i Ü ¼ 9, 6 x B Ð H distilled water (H

2

O), ethylene glycol (HOCH

2

CH

2

OH) x 9 acetic acid (CH

3

COOH)` ¦ 1 : 7 : 2 _ q Ö ¦ Ð D ¥ ½ + Ë # 6 x % i ¦ Ã Ð] j Ð H ethanol (CH

3

CH

2

OH)` ¦ 6 x % i Ü ¼ 9, s M : stock solu- tion _ ] t 0 l x ¸ H 0.2 M Ð × þ % i . Ø ¦ µ 1 Ï" é ¶ « Ñ\ ¦ D ¥ ½ + Ë ô

Ç 6 x B \ ¦ 60

^◦

C \ " f 12r ç ß ì ø Í6 £ x` ¦ r & ¢ - a y 6 x K r

( . ì r ´ ú r « Ñ\ ¦ % 3 l 0 A # / B N ¸ É r \ " f 100

^◦

C

\

" f { 9 Å Ò{ 9 ç ß | ¸ # íl ì r ´ ú ` ¦ ] j ¸ % i . | ¸ ì

r ´ ú \ @ /ô Ç Ä »l Ó ü t _ ì r K x 9 & ñ © _ Ò q t$ í [ þ t` ¦ S X

¦ \ P % o ¸| ` ¦ · ú Ðl 0 A # , TA Instruments _

SDT 2900 ¸4 S q` ¦ s 6 x # DTA/TGA` ¦ Ã º' % i .

|

¸ ) a ì r ´ ú ` ¦ DTA/TGA ÐÂ Ò' % 3 É r õ \ ¦ Ö ¸6 x #

|

¸ô Ç ì r ´ ú ` ¦ 600

^◦

C \ " f 3r ç ß 1 l x î ß / B N l × æ \ " f \ P

%

o # r « Ñ\ ¦ ] j ¸ % i . \ P % o ô Ç ì r ´ ú _ & ñ $ í

`

¦ S X l 0 A # , Philips _ X’pert PW 1827 x-

r] X ì r$ 3 l (CuKα)\ ¦ s 6 x # x- r] X ¸, © Ã º

\

¦ ½ ¨ % i . ¢ ¸ô Ç, \ P % o ô Ç ì r ´ ú _ { 9 ß ¼l x 9 ç H{ 9

¸\ ¦ S X l 0 A # JSM-6700F _ SEM` ¦ 8 £ ¤& ñ

%

i . M¨ossbauer Û ¼& 7 à Ô! 3 É r l % i < Æ& h 1 p x 5 Å q ¸+ þ A [6]

M¨ ossbauer ì rF g l Ð 2 [ % i Ü ¼ 9, " é ¶ É r Dupont r ] j

¾

¡

§ _ Rh F K5 Å q \ [ þ t # Qe H z ´ : r © I _ 40 mCi_ 57Co é ß { 9

` ¦ 6 x % i . r « Ñ_ ª É r 40 mg Ü ¼ Ð % i ¦ r « Ñ _

ç H{ 9 ô Ç ¿ ºa \ ¦ 0 AK f â s 1 u s ¦ ¿ ºa 0.005

u _ Be ó ø Í` ¦ ª \ } " f 6 x % i . $ : rz ´+ « >` ¦ 0

AK " f APD CS-202 displex © u ü < DMX-20 M¨ossbauer vacuum shroud\ ¦ 6 x % i ¦, r « Ñ_ \ P ² ú ` ¦ 0 AK Í t B

Ð He gas\ ¦ í H¨ 8 r ( Ü ¼ 9 1 psi · ú § 4 ` ¦ Ä »t ¸2 ¤

%

i . : r ¸8 £ ¤& ñ É r : r ¸ ¸] X l (Lake Shore DRC-91C + þ

A)\ ¦ s 6 x # 0.05 K_ : r ¸ ¸ _ & ñ x 9 ¸ü < 10−6 torr s © _ / B N ¸\ ¦ Ä »t % i . VSM É r Lake Shore

Fig. 2. X-ray diffraction pattern of α-LiFeO

2

at room temperature. Open circle represents the observed pat- tern; continuous lines represent calculated and difference obs-cal patterns. Ticks markers correspond to the posi- tion of the allowed Bragg reflections.

7300` ¦ s 6 x # # Q : r ¸\ " f ü @Â Ò l © ` ¦ 10 kOe

# l & h : £ ¤$ í ` ¦ 8 £ ¤& ñ % i .

III. ÷ m Ç] M ö+ s ÇÊ Ý õ m Í w ² o

LiFeO

2

ì r ´ ú r « Ñ_ & ñ o 0 p x ô Ç \ P % o : r ¸\ ¦

&

ñ ¦ ] j ¸ ) a a % ¦ ÐÂ Ò' Ä » ¸ ) a 0 q_ Ä »l Ó ü t 1 l x` ¦ ¸

l 0 A # DTA/TGA z ´+ « >` ¦ ' % i Ü ¼ 9, Fig. 1\ LiFeO

2

0 q_ DTA/TGA ì r$ 3 õ \ ¦ ? /% 3 .

244

^◦

C Â Ò H \ " f ' a ¹ 1 Ï÷ & H µ 1 Ï\ P x ß ¼ H > 5 Å q ÷ & H

Ã ºì r K x 9 × æ» ¡ ¤ ½ + Ëì ø Í6 £ x _ Â Òí ß Ó ü t Ð" f Ò q t$ í ) a Ä »l Ó ü t _

è\ _ ô Ç כ Ü ¼ Ð 55 %_ × æ | ¾ Óy è\ ¦ Ã ºì ø Í ¦ e Ü ¼ 9, 550

^◦

C s © _ : r ¸\ " f_ | 9 | ¾ Ó y è H \ O % 3 . s

: r ¸ % ò % i \ " f LiFeO

²

© _ & ñ Ò q t$ í s r H d` ¦ 0 p u

½

+ É Ã º e . 0 A_ õ \ ¦ s 6 x # 600

^◦

C \ " f LiFeO

2

ì

r ´ ú ` ¦ \ P % o % i Ü ¼ 9, © : r \ " f 8 £ ¤& ñ ô Ç x- r] X 8 £ ¤

&

ñ õ É r ½ ¨ ¸_ + þ A © \ O s í H Ã ºô Ç é ß { 9 © _ r « Ñ\ ¦

½

+ Ë$ í ½ + É Ã º e % 3 Ü ¼ 9, s \ ¦ Fig. 2 \ ? /% 3 . ½ + Ë$ í ô Ç r

« Ñ_ ª s : r ì r í 1 p x` ¦ & ñ l 0 A # Rietveld ì r

$ 3

Z O \ _ ô Ç & ñ º ` ¦ Ã º' % i . ì r$ 3 r Fullprof á Ô Ð Õ

ªÏ þ ` ¦ s 6 x % i . þ j7 á x& h Ü ¼ Ð & ñ ) a © Ã º H a = 4.1610 ± 0.0005 ˚ A s % 3 Ü ¼ 9, ø @ ¸\ ¦ ? / H Bragg

R

B

, R

F

H y y 5.56, 3.79 %% i . Fig. 2_ x- r ] X

` ¦ ì r$ 3 ô Ç õ H F m3m _ / B N ç ß ç H` ¦ ° ú H { 9 ~ ½ Ó& ñ + þ

A ½ ¨ ¸ s ü @_ r] X É r Ðs t · ú § ¤Ü ¼ 9 & ñ º _ õ

\

" f Ð1 p w s z ´+ « > u ü < s : r u ¸ ú { 9 u < Ê` ¦ Ðs ¦ e

.

(3)

Fig. 3. SEM micrographs of α-LiFeO

₂

annealed at 600

◦

C. Fig. 4. M¨ ossbauer spectra of α-LiFeO

2

at low tempera- ture.

Fig. 3 É r α-LiFeO

2

& ñ _ $ í © ¸ ª ` ¦ Ðs H SEM 8

£ ¤& ñ õ Ð, 6 £ x| 9 ) a Ñ ü æ H ¸ ª É r 110 nm_ ß ¼l \ ¦

t 9, a % ¦ 0 q ~ ½ Ód \ _ # ] j ) a r « Ñ[ þ t _ + þ A& h + þ

AI \ ¦ Ðs ¦ e 6 £ §` ¦ · ú Ã º e [7]. α-LiFeO

2

_ Curie

Fig. 5. M¨ ossbauer spectra of α-LiFeO

2

at high temper- ature.

: r ¸ü < $ : r \ " f_ p r & h $ í : £ ¤$ í ` ¦ ¸ l 0 A

#

M¨ossbauer Û ¼& 7 à Ô! 3 ` ¦ 4.2 K \ " f 295 K_ : r ¸# 3 0 A

\

" f 2 [ % i Ü ¼ 9, @ /³ ð& h כ [ þ t` ¦ Fig. 4, 5 \ ? /% 3

.

Curie : r ¸ s _ : r ¸\ " f H 2 set( ¾ ú A á ¤;I-site, î ß A

á ¤;II-site) _ / B N" î f ¨ Ã º Ü ¼ Ð K $ 3 % i [8]. s Qô Ç Û ¼

&

7 à Ô! 3 ` ¦ [ jy ì r$ 3 l 0 A # Lorentzian + þ A` ¦ 6

x # þ j è 5 p xZ O Ü ¼ Ð ì r$ 3 % i Ü ¼ 9 [9] s X O > ì r$ 3 ô Ç

õ \ ¦ Table 1 \ Ð# Å Ò ¦ e .

α-LiFeO

₂

_ M¨ossbauer Û ¼& 7 à Ô! 3 É r © : r \ " f 2 line_

× æF G ì r\ P ° ú כ ë ß ` ¦ & H X < s H α-LiFeO

2

_ Curie

: r ¸ © : r s e ` ¦ ? / H כ s . Curie : r ¸\ ¦ S X

l 0 A # M¨ossbauer Û ¼& 7 à Ô! 3 É r 4.2 K \ " f 295 K t : r ¸\ ¦ 7 £ x r v 9 8 £ ¤& ñ ô Ç õ 4.2 K\ " f 55 K

t H 6 line _ / B N" î f ¨ Ã º s ' a8 £ ¤ ÷ &% 3 Ü ¼ Õ ª s © _

: r ¸\ " f H 6 line _ / B N" î f ¨ Ã º s èY > ¦ î r

(4)

Fig. 6. Reduced magnetic hyperfine field H

_hf

(T )/H

_hf

(0) against reduced temperature T /T

_C

for α-LiFeO

₂

. Points marked are the experimental values. The full curve is the Brillouin curve for S = 5/2.

X

< 2 line_ Û ¼& 7 à Ô! 3 ë ß ' a8 £ ¤ ÷ &% 3 Ü ¼ 9, α-LiFeO

²

_ Curie

: r ¸ H 90 ± 3 K Ð & ñ % i . M¨ossbauer ì r$ 3 õ Table 1 \ " f% ! 3 © : r \ " f α-LiFeO

2

_ s $ í | 9 ^ s 1 l x ° ú כ

É r 0.24 mm/s ° ú כ` ¦ & Ü ¼ 9, s H α-LiFeO

2

_ Fe s : r s

t H s : r H Fe

³⁺

e ` ¦ Ð# Å Ò H כ s [8]. 8 £ ¤& ñ

: r ¸ 4.2 K\ " f 7 £ x ½ + ÉÃ º2 ¤ íp [ j l © ° ú כ É r y è

< Ê` ¦ · ú Ã º e % 3 Ü ¼ 9 4.2 K\ " f_ íp [ j l © ° ú כ É r I- site x 9 II-site\ " f 506, 478 kOe, × æF G ì r\ P ° ú כ É r y y 0.02, −0.02 m/s Ð _ % ò \ ¾ ú > z ¤Ü ¼ 9, s H α-LiFeO

2

_ & ñ ½ ¨ ¸ { 9 ~ ½ Ó& ñ + þ A & ñ ½ ¨ ¸e ` ¦ _ p ô Ç

. ¢ ¸ô Ç s $ í | 9 ^ s 1 l x ° ú כ É r 0.37(I-site) ü < 0.36 mm/s(II- site) Ð z ¤ H X < y site_ ^ o = s : r s Fe

³⁺

Ð > r F < Ê` ¦

· ú

Ã º e [10]. s M : 4.2 K\ " f_ I-siteü < II-site_ & h q

H 50 % : 50 % Ð s H α-LiFeO

2

_ & ñ ½ ¨ ¸ { 9 ~ ½ Ó

&

ñ + þ A ½ ¨ ¸e ` ¦ S X ½ + É Ã º e H כ s [8].

Fig. 6 É r α-LiFeO

2

_ íp [ j © ° ú כ_ ¨ î ç H ° ú כ` ¦ : r

¸\ É r o Ð Curie : r ¸ T

^C

\ @ /ô Ç ¨ 8 í ß ) a : r ¸ T /T

C

\ " f_ ] X @ / % ò ¸\ " f_ íp [ j l © H

^hf

(0) \

@

/ô Ç ¨ 8 í ß ) a íp [ j l © H

^hf

(T )/H

hf

(0) _ o ° ú כ` ¦

? / ¦ e . " é ¶ Ü ¼ Ð ³ ðr ) a & h [ þ t s M¨ossbauer z ´+ « >

° ú

כs 9 s \ @ /K z ´ Ü ¼ Ð ³ ðr ) a כ É r spin ° ú כs S = 5/2 Brillouin s : r/ B G Ü ¼ Ð+ ¸ # 3 0 A ? /\ " f " î S X

> ¸ ú Ø Ô ¦ e . Õ ª QÙ ¼ Ð α-LiFeO

²

? /_ Fe

³⁺

s

: r[ þ t É r S = 5/2 Ð high spin © I e ` ¦ · ú Ã º e % 3 [11].

Fig. 7 É r spin wave theory \ _ # α-LiFeO

²

_ T /T

_C

<0.7 # 3 0 A? /_ : r ¸% ò % i \ " f ¨ î ç H íp [ j l

Fig. 7. Fractional change of the average magnetic hyper- fine field, H

_hf

, as a function of (T /T

_C

)

^3/2

for α-LiFeO

₂

.

Fig. 8. Reverse magnetic susceptibility of α-LiFeO

₂

.

É

r : r ¸ 7 £ x < Ê\ y è H X < Õ ª d É r 6 £ § õ ° ú

[12].

H

hf

(T ) − H

hf

(0)

H

hf

(0) = −B

_3/2

T T

C

^3/2

− C

_5/2

T T

C

^5/2

(1)

#

l " f T

^C

H Curie : r ¸s 9 H

^hf

(T ) H : r ¸ T \ " f_

^hf

(0) H ] X @ /% ò ¸\ " f_ íp [ j

5 p x ° ú כÜ ¼ Ð > í ß ô Ç õ α-LiFeO

2

º B

3/2

= 0.36 ± 0.05, C

_5/2

= 0.27 ± 0.05 s % i Ü ¼ 9, s

° ú כ É r & ñ $ í $ í Ó ü t| 9 α-Feü < Ni_ 0.11 x 9 0.12

α-LiFeO

₂

& ñ ? /\ " f 8 ¸ ú # l H d` ¦ · ú Ã º e [13].

`

¦ # 8 £ ¤& ñ ô Ç α-LiFeO

₂

_ % i oÖ ¦` ¦ ? / ¦ e

.

$

3 ô Ç õ Curie-Weiss : r ¸(θ

P

) H @ /| Ä Ì −160 K s % i Ü ¼

(5)

%

$ í

e ` ¦ · ú ¤Ü ¼ 9, Fe

³⁺

_3/2

= 0.36 ± 0.05, C

_5/2

= 0.27 ± 0.05 Ð 8 £ ¤& ñ ÷ &% 3 . ¢ ¸ô Ç Curie-Weiss : r ¸(θ

^P

) H

P

c p 8 ý ò k >

: r ½ ¨ H < ÆÕ ü t < É ª F é ß (KRF-2005-070-C00050)_ t

"

é

¶ \ O \ _ ô Ç כ s 9 s \ y \ ¦ × ¼w n m .

Y

c p w Ã U Ø ô

[1] S. Y. An, I. B. Shim, C. S. Kim, J. Magn. Magn.

Mater. 290-291, 1551 (2005).

[2] X. Wang, L. Gao, F. Zhou, Z. Zhang, M. Ji, C. Tang,

(2005).

[7] P. Vaqueiro, M. P. Cosner-Lppez, and M. A. Lopez- Quintela, J. Solid State Chem. 126, 161 (1996).

[8] M. Tabuchi, S. Tsutsui, C. Masquelier, R. Kanno, K. Ado, I. Matsubara, S. Nasu, and H. Kageyama, J. Solid State Chem. 140, 159 (1998).

[9] S. J. Kim, K. W. Jung C. K. Kim, Hyperfine Inter- actions 156/157, 113 (2004).

[10] M. Tabuchi, C. Masquelier, T. Yakeuchi, K. Ado, I. Matsubara, T. Shirane, R. Kanno, S. Tsutsui, S.

Nasu, O. Nakamura, J. Solid State Ionics 90, 129 (1996).

[11] T. Matsumura, R. Kanno, Y. Inaba, Y. Kawamoto, and M. Takano, J. Electrochemical Soc. 149, A1509 (2002).

[12] S. Y. An, S. W. Lee, D. H. Choi, I. B. Shim, and C.

S. Kim, Phys. Stat. Sol.(c)1 12, 3310 (2004).

[13] C. S. Kim, S. Y. An, Y. R. Uhm, S. W. Lee, Y. B.

Kim and C. S. Kim, J. Appl. Phys. 83, 6929 (1998).

(6)

Magnetic Properties of LiFeO ₂ Powders by a Sol-Gel Process

Seung Wha Lee

Department of Electronic Engineering Chungju National University, Chungju 380-702 Chul Sung Kim

^∗

Department of Physics, Kookmin University, Seoul 136-702 (Received 28 October 2005)

α-LiFeO

2

powders have been prepared by using a sol-gel method. The crystallographic and magnetic properties of the powders were investigated with DTA/TGA, XRD, SEM, M¨ ossbauer spectroscopy, and VSM. The α-LiFeO

2

single-phase is observed in the samples annealed at 600

^◦

C for 3 h in air. The crystal structure of α-LiFeO

2

is found to be cubic with a lattice of a = 4.1610 ± 0.0005 ˚ A. The Curie temperature of α-LiFeO

2

is found to be 90 ± 3 K. The isomer shift values at room temperature are found to be 0.24 mm/s relative to Fe metal, which is consistent with high- spin Fe

³⁺

charge states. The average hyperfine field H

hf

(T ) of the α-LiFeO

2

shows a temperature dependence of [H

hf

(T ) − H

hf

(0)]/H

hf

(0) = −0.36(T /T

C

)

^3/2

− 0.27(T /T

C

)

^5/2

for T /T

C

< 0.7, indicative of spin-wave excitation.

PACS numbers: 74.25.Ha, 75.50.Gg, 76.80.+y

Keywords: M¨ ossbauer spectroscopy, Sol-gel method, LiFeO

2

∗

r] X ì r$ 3 l , Å Ò   & ³p â , M¨ ossbauer ì rF g l x 9  1 l x+ þ Ar « Ñ oÖ ¦8 £ ¤& ñ l \ ¦ s 6 x #   ½ ¨ % i

α-LiFeO

ì  r ´ ú `  ¦ a % ¦ 0 qZ O `  ¦ s 6 x #  ] j ¸ % i  .   & ñ  < Æ& h x 9  l & h $ í | 9 `  ¦ \ P ì  r$ 3  © u , x- 

r] X ì  r$ 3 l , Å Ò     & ³p  â , M¨ ossbauer ì  rF g l  x 9   1 l x+ þ Ar « Ñ  oÖ  ¦8 £ ¤& ñ l \  ¦ s 6 x #    ½ ¨ % i 

. α-LiFeO

é ß { 9  ©  É r 600

C \ " f 3r ç ß  1 l x î ß  / B N l  ×  æ \ " f \ P % o  #  % 3 `  ¦ Ã º e  % 3 Ü ¼ 9, x-  r ] X

ì  r$ 3   õ  α-LiFeO

ì  r ´ ú  É r cubic ½ ¨ ¸\  ¦ &  Ü ¼ 9 s M :     © Ã º a = 4.1610 ± 0.0005 ˚ A s % 3 

. M¨ossbauer Û ¼& 7 à Ô! 3  ì  r$ 3   õ  α-LiFeO

_  Curie  : r  ¸  H 90 ± 3 Ke  `  ¦ · ú  Ã º e  % 3  .  ©  : r \ " f α-LiFeO

_  s $ í | 9 ^ s 1 l x ° ú כ É r 0.24 mm/s ° ú כ`  ¦ &  Ü ¼ 9, s   H α-LiFeO

_  Fe s  : r s  t   H s  : r

  H Fe

_  high spin  © I e  `  ¦  Ð# Å Ò% 3  . α-LiFeO

_  ¨ î ç  H  íp [ j  l  ©  H

(T )  H T /T

<0.7

% ò

% i \ " f [H

(T ) − H

(0)]/H

(0) = −0.36(T /T

)

− 0.27(T /T

)

 Ð spin wave   & ñ ? /\ 

"

f ¸ ú  # l  H  d`  ¦ · ú  Ã º e  % 3  .

PACS numbers: 74.25.Ha, 75.50.Gg, 76.80.+y Keywords: M¨ ossbauer Û ¼& 7 à Ô! 3 , a % ¦ 0 q ] j ¸Z O , LiFeO

I. " e Â ] Ø

o

½ ¢ § s  : r  t   H \  -t x 9  ¸ Z  }  ¦  l  ~ ½ Ó  Ö  ¦ s  ± ú  Ü

¼ 9 1 l x{ 9  ^ & h , Á º>  { ©  6 x | ¾ Ós   H  © & h `  ¦ t  ¦ e   .

÷

 r ë ß   m  , B j ¸o  ´ òõ  \ O # Q" f  6 x  ©  ¼ # o   ¦ Ã º

"

î s  U ´ .  ¸à Ô· ¡ ¤, Ö  r ï 8, Ê ë@ /  o 1 p x þ j   H ] j¾ ¡ § _   è + þ

A o\       t    ^  ] j¾ ¡ § \  p u   H % ò  ¾ Ós  & &  Ü ¼ 9, Õ ª\     Â Ò¾ ¡ § _   â | ¾ Ó oü < $   èq   § 4 oü <  8Ô  ¦

#

Q   t _   è+ þ A oü < é ß 0 A  & h { ©  @ /6 x | ¾ Ó o ´ ú § É r  ' a d   s

 ÷ & ¦ e    [1,2]. : £ ¤ y , o ½ ¢ § (Li) õ  ^ o = (Fe) í ß  oÓ ü t  LiFeO

ü < LiFe

O

\  @ /ô  Ç   ½ ¨  H o ½ ¢ § s  : r  t _  cath- ode Ó ü t| 9  Ð_  6 £ x6 x õ   Å (garnet : Y

Fe

O

)`  ¦ @ /  

#

  Ð  $ § 4 ô  Ç   _  s ß ¼ Ð  6 £ x6 x Â Ò¾ ¡ § > hµ 1 Ï Ð  

#  ´ ú § É r   ½ ¨ s À Ò# Qt  ¦ e    [3,4]. LiFeO

  H ½ + Ë$ í



¸| x 9 ~ ½ ÓZ O \     α-LiFeO

, β-LiFeO

, x 9 γ-LiFeO

_  3 t    & ñ ½ ¨ ¸\  ¦ t  ¦ e   . α-LiFeO

  H   d   { 9 ~ ½ Ó

&

ñ (fcc cubic) ½ ¨ ¸ Ð, Li

ü < Fe

s  : r É r Ô  ¦ ½ ©g Ë :& h Ü ¼ Ð

E-mail: [email protected] Tel: 02-910-4752, Fax: 02-910-5170

¼

1 Ï  ^   o \  ¦ & h Ä »  ¦ e  Ü ¼ 9, / B N ç ß ç  H É r F m3m s  .

γ-LiFeO

(tetragonal, I41/amd)  H Li

ü < Fe

s  : r s  ¼ 1 Ï



 ^  ½ ¨ ¸\ " f ½ ©g Ë :& h   | 9 " f\  ¦ f  Ü ¼ Ð   & ñ     @ / g A$ í s  ×  ¦ # Q[ þ t # Q { 9 ~ ½ Ó& ñ ½ ¨ ¸\ " f  ~ ½ Ó& ñ ½ ¨ ¸ Ð   



 " f % 3 # Q  . ¢ ¸ô  Ç, β-LiFeO

(monoclinic, C2c)  H α- LiFeO

\ " f γ-LiFeO

 Ð     H ×  æ ç ß õ & ñ \ " f + þ A$ í  ) a  [5]. LiFeO

Ó ü t| 9 _    l & h : £ ¤$ í  É r ´ ú § É r   ½ ¨ s À Ò# Qt 



¦ e  Ü ¼   l & h $ í | 9 \   ' a ô  Ç   ½ ¨  H ´ ú §s  Â Ò7 á ¤ ô  Ç z ´& ñ s

 . s \   : r   ½ ¨\ " f  H a % ¦ 0 q ] j ¸Z O Ü ¼ Ð LiFeO

r] X ì r$ 3 l , Å Ò & ³p â , M¨ ossbauer ì rF g l x 9 1 l x+ þ Ar « Ñ oÖ ¦8 £ ¤& ñ l \ ¦ s 6 x # ½ ¨ % i

ì r ´ ú ` ¦ a % ¦ 0 qZ O ` ¦ s 6 x # ] j ¸ % i . & ñ < Æ& h x 9 l & h $ í | 9 ` ¦ \ P ì r$ 3 © u , x-

r] X ì r$ 3 l , Å Ò & ³p â , M¨ ossbauer ì rF g l x 9 1 l x+ þ Ar « Ñ oÖ ¦8 £ ¤& ñ l \ ¦ s 6 x # ½ ¨ % i

. α-LiFeO

é ß { 9 © É r 600

C \ " f 3r ç ß 1 l x î ß / B N l × æ \ " f \ P % o # % 3 ` ¦ Ã º e % 3 Ü ¼ 9, x- r ] X

ì r$ 3 õ α-LiFeO

ì r ´ ú É r cubic ½ ¨ ¸\ ¦ & Ü ¼ 9 s M : © Ã º a = 4.1610 ± 0.0005 ˚ A s % 3

. M¨ossbauer Û ¼& 7 à Ô! 3 ì r$ 3 õ α-LiFeO

_ Curie : r ¸ H 90 ± 3 Ke ` ¦ · ú Ã º e % 3 . © : r \ " f α-LiFeO

_ s $ í | 9 ^ s 1 l x ° ú כ É r 0.24 mm/s ° ú כ` ¦ & Ü ¼ 9, s H α-LiFeO

_ Fe s : r s t H s : r

H Fe

_ high spin © I e ` ¦ Ð# Å Ò% 3 . α-LiFeO

_ ¨ î ç H íp [ j l © H

(T ) H T /T

% i \ " f [H

Ð spin wave & ñ ? /\

f ¸ ú # l H d` ¦ · ú Ã º e % 3 .

PACS numbers: 74.25.Ha, 75.50.Gg, 76.80.+y Keywords: M¨ ossbauer Û ¼& 7 à Ô! 3 , a % ¦ 0 q ] j ¸Z O , LiFeO

½ ¢ § s : r t H \ -t x 9 ¸ Z } ¦ l ~ ½ Ó Ö ¦ s ± ú Ü

¼ 9 1 l x{ 9 ^ & h , Á º> { © 6 x | ¾ Ós H © & h ` ¦ t ¦ e .

r ë ß m , B j ¸o ´ òõ \ O # Q" f 6 x © ¼ # o ¦ Ã º

î s U ´ . ¸à Ô· ¡ ¤, Ö r ï 8, Ê ë@ / o 1 p x þ j H ] j¾ ¡ § _ è + þ

A o\ t ^ ] j¾ ¡ § \ p u H % ò ¾ Ós & & Ü ¼ 9, Õ ª\ Â Ò¾ ¡ § _ â | ¾ Ó oü < $ èq § 4 oü < 8Ô ¦

Q t _ è+ þ A oü < é ß 0 A & h { © @ /6 x | ¾ Ó o ´ ú § É r ' a d s

÷ & ¦ e [1,2]. : £ ¤ y , o ½ ¢ § (Li) õ ^ o = (Fe) í ß oÓ ü t LiFeO

\ @ /ô Ç ½ ¨ H o ½ ¢ § s : r t _ cath- ode Ó ü t| 9 Ð_ 6 £ x6 x õ Å (garnet : Y

)` ¦ @ /

Ð $ § 4 ô Ç _ s ß ¼ Ð 6 £ x6 x Â Ò¾ ¡ § > hµ 1 Ï Ð

# ´ ú § É r ½ ¨ s À Ò# Qt ¦ e [3,4]. LiFeO

H ½ + Ë$ í

¸| x 9 ~ ½ ÓZ O \ α-LiFeO

_ 3 t & ñ ½ ¨ ¸\ ¦ t ¦ e . α-LiFeO

H d { 9 ~ ½ Ó

ñ (fcc cubic) ½ ¨ ¸ Ð, Li

s : r É r Ô ¦ ½ ©g Ë :& h Ü ¼ Ð

1 Ï ^ o \ ¦ & h Ä » ¦ e Ü ¼ 9, / B N ç ß ç H É r F m3m s .

(tetragonal, I41/amd) H Li

s : r s ¼ 1 Ï

^ ½ ¨ ¸\ " f ½ ©g Ë :& h | 9 " f\ ¦ f Ü ¼ Ð & ñ @ / g A$ í s × ¦ # Q[ þ t # Q { 9 ~ ½ Ó& ñ ½ ¨ ¸\ " f ~ ½ Ó& ñ ½ ¨ ¸ Ð

" f % 3 # Q . ¢ ¸ô Ç, β-LiFeO

(monoclinic, C2c) H α- LiFeO

\ " f γ-LiFeO

Ð H × æ ç ß õ & ñ \ " f + þ A$ í ) a [5]. LiFeO

Ó ü t| 9 _ l & h : £ ¤$ í É r ´ ú § É r ½ ¨ s À Ò# Qt

¦ e Ü ¼ l & h $ í | 9 \ ' a ô Ç ½ ¨ H ´ ú §s Â Ò7 á ¤ ô Ç z ´& ñ s

. s \ : r ½ ¨\ " f H a % ¦ 0 q ] j ¸Z O Ü ¼ Ð LiFeO

\ ¦ ] j

¸ # DTA/TGA, x- r] X l , Å Ò & ³p â (SEM)

¦ s 6 x # \ P % o ¸| , & ñ ½ ¨ ¸ x 9 { 9 _ ß ¼l \ ¦ ¸

% i Ü ¼ 9, M¨ossbauer ì rF g l , 1 l x r « Ñ oÖ ¦8 £ ¤& ñ l

¦ : x # Li

s : r[ þ t _ site ì r í ¸ x 9 l & h $ í

` ¦ ¸ % i .

% ¦ 0 q ] j ¸Z O Ü ¼ Ð LiFeO

ì r ´ ú ` ¦ ½ + Ë$ í l 0 Aô Ç Ø ¦ µ 1 Ï

¶ « Ñ Ð" f H í H ¸ 99.99 %_ iron nitrate (Fe(NO

O) x 9 99.99 %_ lithium acetate (CH

Li)\ ¦ 6

x % i Ü ¼ 9, 6 x B Ð H distilled water (H

COOH)` ¦ 1 : 7 : 2 _ q Ö ¦ Ð D ¥ ½ + Ë # 6 x % i ¦ Ã Ð] j Ð H ethanol (CH

OH)` ¦ 6 x % i Ü ¼ 9, s M : stock solu- tion _ ] t 0 l x ¸ H 0.2 M Ð × þ % i . Ø ¦ µ 1 Ï" é ¶ « Ñ\ ¦ D ¥ ½ + Ë ô

Ç 6 x B \ ¦ 60

C \ " f 12r ç ß ì ø Í6 £ x` ¦ r & ¢ - a y 6 x K r

( . ì r ´ ú r « Ñ\ ¦ % 3 l 0 A # / B N ¸ É r \ " f 100

" f { 9 Å Ò{ 9 ç ß | ¸ # íl ì r ´ ú ` ¦ ] j ¸ % i . | ¸ ì

r ´ ú \ @ /ô Ç Ä »l Ó ü t _ ì r K x 9 & ñ © _ Ò q t$ í [ þ t` ¦ S X

¦ \ P % o ¸| ` ¦ · ú Ðl 0 A # , TA Instruments _

SDT 2900 ¸4 S q` ¦ s 6 x # DTA/TGA` ¦ Ã º' % i .

¸ ) a ì r ´ ú ` ¦ DTA/TGA ÐÂ Ò' % 3 É r õ \ ¦ Ö ¸6 x #

¸ô Ç ì r ´ ú ` ¦ 600

C \ " f 3r ç ß 1 l x î ß / B N l × æ \ " f \ P

o # r « Ñ\ ¦ ] j ¸ % i . \ P % o ô Ç ì r ´ ú _ & ñ $ í

¦ S X l 0 A # , Philips _ X’pert PW 1827 x-

r] X ì r$ 3 l (CuKα)\ ¦ s 6 x # x- r] X ¸, © Ã º

¦ ½ ¨ % i . ¢ ¸ô Ç, \ P % o ô Ç ì r ´ ú _ { 9 ß ¼l x 9 ç H{ 9

¸\ ¦ S X l 0 A # JSM-6700F _ SEM` ¦ 8 £ ¤& ñ

i . M¨ossbauer Û ¼& 7 à Ô! 3 É r l % i < Æ& h 1 p x 5 Å q ¸+ þ A [6]

M¨ ossbauer ì rF g l Ð 2 [ % i Ü ¼ 9, " é ¶ É r Dupont r ] j