- Vung tin sd trung binh: trong vung tin sd nay anh hudng cua dien dung hinh hoc khdng con Khi đ tdng trd dugc quyét dinh bdi dien dung cua ldp kep hinh thanh
n. K fT QUA KHAO SAT DO DAN ION CUA MANG M6 NG LiMÔBANG PHUONG PHAP P H 6 TONG T R 6 DOI V 6 l
Mang LiMn204 dugc che tao bing phucmg phap bdc bay chiim tia dien tu [2] va u nhiet ngay sau khi tao mang tai 450 °C trong 1 gid. De tien hanh nghien cuu cac tfnh chát dien cua mang, Idp dien cue bac hoac vang dugc phu len tren mang bing phuang phap bdc bay nhiet theo cáu hinh banh kep (ITO/LiMn204/Ag).
Chieu day ciia mang mong la yéu td quyet dinh nhieu tfnh chát dien va quang ciia mang mdng. Khao sat su phu thudc ciia dac trung phd tdng trd vao chieu day se cho ta biét them nhieu thdng tin hiiu fch de ly giai cac tfnh chát dien ciia mang mdng din ion LiMn204. Két qua thuc nghiem do phd tdng trd phu thudc chieu day cua cac miu cd dien tfch 1 cm^ va chieu
day tir 0,4 dén 1,0 \im dugc
trinh bay tren Hinh 4. Thdng thudng, đ'i vdi cung loai vat lieu thi khi chieu day cua miu giam xudng, R^-t ciing giam theọ Tuy nhien két qua thuc nghiem cho tháy chieu day ciia mang giam dén mdt gia tri tdi han nao đ thi phd tdng trd khdng CO hep lai ma lai md rdng ra mdt each bát thudng, dieu
nay chiing td R^^ da tang len
dang kẹ Su bién đi bát thudng
40-
20-
20 40 Z (Ohm) Z (Ohm)
60 80
Hinh 4. Gian 66 Cole-Cole ciia mang LiMn.Oj voi
«H <-»» rviiutt iitR; va cong nghẹ Vien Khoa hoc vk Cdng nghe Viet Nam, /// (2005) ??
trong Rj.( nhan dugc t^ phep do cd the giai thfch la do khi mkng qua mdng thi dien trudng tren mang se la qua Idn, do đ dien dung ldp Helmholtz se cd anh hudng cue manh, lam thay đi hin dac trung ciia phd tdng trd cua mlu dọ
Anh hudng n^y cang trd nen ro ret hem khi chieu day miu cang nhd va tin sd do cang th^p. Tren Hinh 5 la dudng cong Cole - Cole (phd tdng trd) ciia mang LiMn204 cd chieu day 0,3 ^im. Cac dudng bi^u dien Cole - Cole ciia phd tdng trd nhan dugc gin nhu bi tach thanh hai nira dudng trdn. Su xuS^t hien cung trdn thii hai d vung tin sd tháp dugc xac dinh la do đng gdp ciia cac qua trinh xay ra tren be mat tiép xiic giiia mang va dien cuẹ
Tir Hinh 5 cd thd nhan th^y vdi su xu^t hien ca hai cung trdn thi viec xac dinh cac tham sd theo so đ mach tuong duang cho phd mdt niia dudng trdn nhu tren la khdng cdn chfnh xac. Ndi each khac, đi vdi cac mang mdng cd 0,3 fim thi sa đ mach tuang duong ap dung cho mang day la khdng con phu
hgp. Do vay di xac dinh gia tri đ
din ion ciia vat lieu mang mdng cin phai cd so đ tuang duang khac.
Viec phan tfch sa d6 mach tuang
duang cho cac miu mang mdng phiic tap hon rát nhieu, vi trong
trudng hgp mang qua mdng thi anh hudng ciia cac qua trinh tren be mat bien tiep xiic giiia mang va cac dien cue se đng vai tro dang kẹ De cd the dua ra sa đ tuang duong phu hgp, chiing tdi da sir dung chuong trinh phan tfch sd lieu tdng trd ap dung cho phuang phap triing khft phd thuc nghiem vdi dudng cong ly thuyet.
Chuong trinh nay cho phep chiing ta lua chon cac mach tucmg duong vdi cac thanh phin va each mic da dang. Mdi mdt mach tuong ducmg se cd dudng cong ly thuyét tucmg iing, tren co sd đ chiing tdi da tim ra mach tuong duang cho dudng cong ly thuyét phu hgp tdt nhát vdi sd lieu thuc nghiem. Ket qua triing khft phd da dua ra sa đ tucmg duang ciia miu dugc md ta tren Hinh 6.
Hinh 5. Gian 66 Cole - Cole nhan dugc tren mang
LiMn204 CO chieu d^y 0,3 )im 6 trong dai l^n s6 lir 10 mHz ^1 MHz. R I (I) C l R2 0 (II) C3 R4 (III)
.«p V,... .viiuii iiuc va »^ong ngne, Vien Khoa hgc va Cdng nghe Viet Nam, /// (2005) ?? Mach tuang duang nay cd dang gin gidng vdi md hinh ciia Gohr. Trong sa đ
nay cd thi chia ra thanh ba thanh phin phu thudc tin sd khac nhaụ Dd la:
• Tlianh phin (I) chi cd mdt dien trd RI mic ndi tiep vdi toan mach bao gdm dien trd ciia dien cue ITO va dien trd day din, khdng phu thudc vao tin sd dọ
• Thanh phin (III) dac trung dap iing viing tin sd cao, đ la cac dai lucmg lien quan den tfnh chát din ion ciia mang. Thanh phin nay gdm tu dien C3 - xu^t hien giua
hai dien cue song song vdi dien trd R4 - dien trd khdi cua mang UMnjO,, dai
lugng dac trung cho đ din ion ciia mang.
• Thanh phin (II) dac trung phin đng gdp cua cic qua trinh be mat ldp tiep xiic giiia mang va cae dien cue, lien quan den dac trung dap viing tin sd th^p, trong đ R2 la dien trd dac trung qua trinh hip thu be mat; R3 la dien trd chuyen dich dien tfch, phan anh qua trinh chuydn dich ion qua ldp bien phan each. C2 la dien dung ciia ldp Helmholtz va C3 la dien dung do qua trinh chuyen dich dien tfch gay nen. Ngoai ra cdn cd thanh phin pha khdng đi Q, đ la dai lugng gay ra bdi cac hieu ling hinh hgc nhu cac hieu iing bien tiép xiic, kfch thudc hat v.v... Gia tri tdng trd cua nd dugc xac dinh bdi: Z(Q) = A*(jo3)"". Vdi n = 0 thi Q la dien trd thuin, Q cd dang ciia tdng trd Warburg khi n = 0,5 va ciia mdt tu dien khi n = 1.
Ap dung sa đ tuong duong nhu tren, chiing tdi da nhan dugc dudng cong ly thuyét va thuc nghiem vdi su triing khft rSit tdt. Ket qua triing kbit dugc trinh bay tren Hinh 5. Cac gia tri cu the tuong iing vdi cac thanh phin tren so đ mach tuang duang dugc xac dinh va liet ke trong Bang 1.
Bang 1. Cac tham sd cua pho tong trd cua mang mong LiMn204 xac dinh tir phep triing kbit pho ly thuyet vdi sd lieu thuc nghiem
(I) Rl(n) Rl(n) 207 (III) R2(Q) -2,35 R3(Q) 34 Cl(^F) 10"^ C2(^F) 0,431 Q ĂQ) 0,185.10-' n 0,55 (lU) R4(n) 4,33 C3(^F) 0,118 Tii cac két qua tren chiing tdi xac dinh dugc dien trd khdi cua mang LiMn204 trong trudng hgp nay la R3 = 4,33 Q. Miu cd chieu day 0,3 |im va dien tfch 1cm". Sir dung cdng thiic (16) do din ion cua mang da dugc xac dinh a = 5 xlO"^ Scm"'. Gia tri do din xac dinh trong miu mdng nhu d trudng hgp nay hoan toan phu hgp vdi gia tri do din ciia cac miu daỵ
HỊ KET LUAN
Bing viec phan tfch va ap dung phuang phap phd tdng trd, tfnh chat din ion cua mang mdng LiMn.Oi da dugc nghien ciiụ Su dung sa đ tuong ducmg thich hcyp cho cac miu day va mdng khac nhau cho phep loai bd anh hudng cua ldp Helmholtz (ldp bien tiep xiic giiia mang va dien cue).
Dd din ion cua mang LiMojOj che tao bing phucmg phap bdc bay chiim tia dien tu dugc xac dinh tir thuc nghiem do phd tdng trd va trung khft vdi dudng cong tinh
toan, G ^ 5 xlÓ^ Scm'. Gia tri nay hoan toan phii hgp vdi ket qua da cdng bd ve do
din ion liti cua cac vat lieu dxit spinel d dang khdi (LiM.Oj vdi M la cac nguyen td
iạ\j cm R.noa noc va L^ng ngne, Vien Khoa hoc va Cdng nghe Viet Nam, /// (2005) ??
Ldi cam on
Cac tac gia chan thinh cam cm Hdi đng KHTN vd su hd trg kinh phf Nghien ciiu CO ban trong nam 2004.
Tai li^u tham khao
[1].M. F. Daniel, B. Desbat and J. C. Lassegues, Infrared and Raman spectroscopies
ofRf-sputtered tungsten oxide fdms, Journal of solid state chemistry, 73, (1988), p
127-139.
[2].Pham Duy Long, Nguyen Nang Dinh, Le Van Hdng, Dd Xuan Mai, Cdc tinh chat
dien, quang cua mdng mong LiMn204 che tao bang phuang phap bdc bay chum
tia dien tic, trong: Nhiing v^n de hien dai eiia vat 15^ ch^t rin. Tap II-A, (Tuy^n tap
bao cao tai Hdi nghi Vat ly Ch^t rin toan qudc lin thu: III - Nha Trang 8/2001), Nha xuaft ban KHKT, Ha Ndi - 2003, tr. 245-252.
[3].Gary S. Kanner and Darryl P. Butt, Raman and electrochemical probes of the dissolutin kinetics of tungsten in hydrogen peroxide, J. Phys. Chem. B, 102 (1998) p 9501-9507.
[4].S. Papaethimious, G. leftheriotis, P. Yianoulis, Study of electrochromic cell incorporating W03, Mo03, W03-Mo03 and V205 coating. Thin solid films, 343/344 (1999) p. 183-186.
[5],J. M. Amarilla, F. Tedjar and C. Poisignon, Influence of KOH concentration on the Y - Mn02 redox mechanism, Electrochimica Acta, Vol. 15 (1994) p. 2321 - 2331.
wiii Áviiua iiuu va t^ng nghe, Vien Khoa hgc va Cdng nghe Viet Nam, /// (2005) 97
APPLICATION OF IMPEDANCE SPECTROSCOPY METHOD FOR . CHARACTERISATION OF IONIC CONDUCTIVITY OF . CHARACTERISATION OF IONIC CONDUCTIVITY OF
LiMn204 FILMS
Nguyen Nang Dinh
Faculty of Technology, Vietnam National Universitỵ Hanoi
Le Dinh Trong
Faculty of Physics, Hanoi Pedagogical University Nọ2, Xuan Hoa, Vinh Phuc
Impedance spectroscopy (IS) technique has been analyzed and applied to measure the ionic conductivity of the films. Equivalent schemes were used for two eases of characterizations, namely for a standard three-electrodes and for a two-electrodes cells. For superionic thin solid films it is necessary to characterize IS by using the two-electrodes cell, where superionic material is deposited between two thin-film electrodes. In this ease Helmholtz layer can affect to the conductivity during the measurement. To eliminate the influence of this layer, equivalent schemes were chosen with separation of three frequency zones and to fit the theoretical curves to experimental datạ Then the best curve fitted with two to three circles is taken and elaborated to determine all the parameters of the scheme, and R3 in particular.
The samples for IS measurements are of LiMn204 crystalline thin films prepared by electron beam deposition. From XRD analysis it has been seen that the films have the same crystalline structure of the bulk samplẹ The ITO transparent conducting film was used as the substrate for the deposition, consequently it was served as the first electrode for IS characterization. Vacuum Ag-coating was served as the second onẹ Thus, samples with a design of ITO/LiMn204/Ag were used to measure on an AutoLab-Potentiostat-PGS-30 system that is available in the Institute of Materials Science, VAST. The experimental data were fitted with the curve obtained from the best equivalent schemẹ From these curves the ionic conductivity at room temperature was found t o b e o f a = 5x10-^ Scm'.
• M f t t ^ ^ i } » / » J V I iiurui ocience, /// (2005), ??