利用化學控制合成新穎電子/離子作用氧化物及其特性分析(1/3)

行政院國家科學委員會專題研究計畫 期中進度報告

利用化學控制合成新穎電子/離子作用氧化物及其特性分析

(1/3)

計畫類別： 個別型計畫

計畫編號：

NSC91-2113-M-002-044-執行期間： 91 年 08 月 01 日至 92 年 07 月 31 日

執行單位： 國立臺灣大學化學系暨研究所

計畫主持人： 劉如熹

計畫參與人員： 詹丁山、王健源、張嵩駿、紀喨勝、林欣瑋、陳浩銘、周大為、

林益山

報告類型： 精簡報告

報告附件： 出席國際會議研究心得報告及發表論文

處理方式： 本計畫可公開查詢

中

華

民

國 92 年 5 月 29 日

行政院國家科學委員會補助專題研究計畫成果

報告

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※ 利用化學控制合成新穎電子/離子作用氧化物

※

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及其特性分析(1/3)

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※※※※※※※※※※※※※※※※※※※※※※※

※※

計畫類別：þ個別型計畫 □整合型計畫

計畫編號：NSC 91-2113-M-002-044

執行期間：91 年 8 月 1 日 至 92 年 7 月 31 日

計畫主持人：劉如熹

本成果報告包括以下應繳交之附件：

□赴國外出差或研習心得報告一份

□赴大陸地區出差或研習心得報告一份

þ

出席國際學術會議心得報告及發表之論文各一份

□國際合作研究計畫國外研究報告書一份

執行單位：台灣大學化學系

中

華

民

國

九 十 二 年

五

月 二 十 七 日

行政院國家科學委員會專題研究計畫成果報告

利用化學控制合成新穎電子/離子作用氧化物及其特性分析

(1/3)

Synthesis by Chemical Contr ol and Char acter ization

of New Electr onic/Ionic Oxides

計畫編號：NSC 91-2113-M-002-044

執行期限：91 年 8 月 1 日至 92 年 7 月 31 日

主持人：劉如熹 教授（台灣大學化學系）

計畫參與人員：詹丁山、王健源、張嵩駿、紀喨勝、

林欣瑋、陳浩銘、周大為、林益山

（台灣大學化學系）

一、中文摘要 隨科技之進步，資訊產業之發展也日新月異， 資訊產品愈來愈多樣化，且持續有各式各樣之紀錄 媒體相繼研發中，藉以滿足人類對大量資料儲存與 紀 錄 上 之 需 求 。 自 1995 年 具 穿 隧 式 磁 電 阻 (tunneling magnetoresistance; TMR)效應之材料得 到突破性之進展，短短幾年內，其磁性感應度即提 高一倍以上。TMR 於室溫時之 25~50 % 磁電阻 值 ， 遠 遠 高 於 傳 統 之 巨 磁 電 阻 (giant magnetoresistance; GMR)材料(室溫~ 10 %)，使其對 於各式紀錄媒體而言更具發展潛力。有鑑於此，本 研究乃探討於 Sr2FeMoO6 (Sr2BB′O6)雙層鈣鈦礦化 合物中，固定鹼土族鍶離子，藉由不同 3d、4d與 5d之過渡金屬離子，取代 B 或 B′之位置。計合成

以 3d5(Fe)為主之 Sr2FeMoO6 (Fe

3+_：Mo5+_⇔ 3d5： 4d1)與 Sr2FeWO6 (Fe3+：W5+⇔ 3d5：5d1)系統，進 而研究其晶體結構、磁性、電性等性質，以期開發 最佳配置且特性卓越之穿隧磁電阻材料。 關鍵詞：穿隧式磁電阻、巨磁電阻、雙層鈣鈦礦、 Sr2FeMoO6、Sr2FeWO6. 一、Abstract

By the technological improvement, the information development is changing with the passing day and various several mediums are keeping researching to satisfy the request of data’s storage and recordation. Since 1995 materials of TMR (tunneling magnetoresistance) effect were improved evidently, in few years it’s magnetic induction rose double. TMR materials show much higher MR% (about 25~50%) than traditional GMR materials (about 10%) under room temperature, so it is considered to apply to MR sensor of the magnetic recording industry. Accordingly,

in

this research the Sr2FeMoO6

(Sr2BB′O6) double perovskites compounds were

fabricated by keeping the stoichiometry of the alkaline earth strontium ion and displacing the position of B or B′ with different 3d, 4d and 5d transition metals. Therefore, based syatems of 3d5(Fe) systems of Sr2FeMoO6 (Fe3+：Mo5+ ⇔ 3d5：4d1) and

synthesized. Moreover, their crystal structures, magnetic and electrical properties have been studied which may lead to develop the optimal composition and excellent properties of the new TMR materials. Keywords: tunneling magnetoresistance (TMR)、 giant magnetoresistance (GMR)、double perovskites、Sr2FeMoO6、Sr2FeWO6

二、緣由與目的

In ordered double perovskites denoted as A2BB

O6 (where A = alkaline-earth or rare-earth ion), the

transition metal sites are occupied alternately by different cations B and B. It is known that the differences in the valence and size between the B and B cations in double perovskites type compounds are crucial to controlling the physical properties.1-2 Among them, Sr2FeMoO6 have been known as

potential magnetoresistance materials, which show large low-field tunneling magnetoresistance (TMR) at room temperature (RT).3 The magnetic structure of Sr2FeMoO6 was attributed to an ordered arrangement

of parallel Fe3+ (3d5, S = 5/2) magnetic moments, antiferromagnetically coupled with Mo5+ (4d1, S = 1/2) spins. Since Fe3+ is in the high spin state, its d orbitals are split into spin up and spin down states. Sleight et al.4 proposed that if the spin down 3d orbitals of Fe have similar energy to the 4d orbitals of Mo, they can form a narrow band and provide the conduction mechanism. The band calculations, which show a mixing of the spin-down O 2p, Fe 3d and Mo 4d bands at the Fermi level supported this mechanism.3,5-6 Other Fe-based ordered double perovskites A2FeMO6 (A = Ba, Sr, Ca; M= Mo, Re)

have also been reported to have half-metallic nature and high Tc .7-13

On the other hand, recently, the further study to figure out some effects of Fe/Mo disorder on magnetic and electrical properties in Sr2FeMoO6.

14,15

For ordered state, the Fe3+ and Mo5+ ions antiferromagnetically coupled and give rise to ferromagnetic metal with saturated magnetization Ms = 4 ìB. However, most of the experiments data

showed a reduced Ms. This fact seems to be related to antisite defects, where some of the Fe and Mo ions interchange their crystallographic positions. The actual degree of Fe/Mo order depends on synthesis conditions. As a rule of thumb, increased order may be obtained with increased synthesis temperature or treatment time.16,17

In relation to the electronic configurations of the Sr2FeMoO6, the average valence for Fe was also

been found to be intermediate between high spin configurations values of Fe2+ and Fe3+ from MÖssbauer spectroscopy studies.

8,18,19

This suggests that both electronic configurations with Fe2+ and Fe3+ must be considered as degenerate, with the final state being a combination of both configurations.

Conversely, Sr2FeWO6 is know as an

antiferromagnetic insulator with TN of 16-37 K,

where Fe2+ ions is in the high-spin state (S = 2), and W6+ ion (5d0) is in the non-magnetic state.20-22 This

would give rise to a complete localization of the valence electrons, explaining the decrease in conductivity. Therefore, the fundamental question is why the W case so different from the Mo case despite the fact that W is 5d analogue of 4d Mo in the row of the Periodic Table?

In this research we report the synthesis and characterization of the Sr2FeMO6 (M = Mo, W)

samples with particular focus on the effect of the variation of B -site transition metal on the physical properties. We will show that the stronger 2p(O)-4d(Mo) hybridization compared with the 2p(O)-5d(W) hybridization is the main source of the difference between Sr2FeMoO6 and Sr2FeWO6.

三、研究方法

Sample Pr epar ation. The samples of Sr2FeMO6 (M = Mo, W) were prepared by solid state

reaction. Stoichiometric mixtures of high purity oxides SrCO3, Fe2O3 or MoO3 and WO3 were

calcined at 800 °C for 12 h in air. The obtained powders were ground and pressed into pellets (15 mm in diameter and 3 mm in thickness). The pellets of Sr2FeMoO6 were then sintered at 1000 °C for 38 h

in a 5 % H2 / N2 gas mixture. However, the pellets of

Sr2FeWO6 were sintered at 1200 °C for 18 h in a 5 %

H2 / N2 gas mixture.

Char acter ization. X-ray diffraction (XRD)

measurements were carried out on a SCINTAG (X1) diffractmeter (Cu Kα radiation, λ = 1.5406 Å ) at 40 kV and 30 mA. The GSAS program23 was used for the Rietveld refinements in order to obtain information on the crystal structures of Sr2FeMO6 (M

= Mo, W). A pseudo-Voigt function was chosen to generate the line shape of the diffraction peaks. In the final runs, the positional coordinates, isotropic thermal factors, and anti-site disorder of Fe、Mo and

W atoms were refined. Scanning electron

micrographs (SEMs) were measured at room temperature by a Philips XL30 SEM equipped with a field emission gun at 15 kV. Electron diffraction (ED) and high resolution transmission electron microscopy (HRTEM) were carried out using a JEOL 4000EX electron microscope operated at 400 kV. Image simulation was made using CaRIne software. The samples for microscopic measurement were dispersed in alcohol before being transferred to the carbon coated copper grids. The resistively measurements at zero field [(ñ(T))] and under a magnetic field [(ñ(H))] were performed with a Quantum Design PPMS (physical properties measurements system), using the conventional four-probe technique, under magnetic fields up to 3 T. Magnetization measurements were performed on a SQUID magnetometer from 0 to 350 K in field-cooled (FC) and Zero-field-cooled (ZFC) modes.

X-r ay Absor ption Measur ements. X-ray

absorption near edge structure (XANES)

measurements at Fe-L23 were performed at the

national synchrotron radiation research center (NSRRC) in Hsinchu, Taiwan with an electron beam

energy of 1.5 GeV and a maximum stored current of 240 mA. All the measurements were performed at room temperature. The XANES measurements at the Fe-L23 edge were performed at the 6-m high-energy

spherical grating monochromatic (HSGM) beamline BL20A. The sample were in powder form, attached on conducting tape, and then put into an ultrahigh vacuum chamber (10-9 Torr) in order to avoid surface contamination. The spectra were recorded by measuring the sample current. The incident photon flux (I0) was monitored simultaneously by using a Ni

mesh located after the exit slit of the monochromatic beam. The reproducibility of the adsorption spectra of the same sample in different experimental runs was found to be extremely good.

Band str uctur e calculations. Band structures of

tetragonal (Sr2FeMoO6) and orthorhombic

(Sr2FeWO6) were calculated using the all-electron

full-potential theory linear augmented plane wave (FLAPW) method.24 These calculations were based on first-principles density functional theory (DFT) with the generalized gradient approximation (GGA) to the exchange-correlation potential. Fe 4s4p3d, Mo 5s5p4d, W 6s6p5d, O 2s2p, and Sr 5s5p5d were treated as band states. The shallow Fe:3s3p, Mo:4s4p, W:5s5p, and Sr:4s4p orbitals were also treated as band states by using the so-called local orbitals. A large number (~120/atom) of augmented plane waves were used. The wave function, charge densities, and potentials were expanded in terms of the spherical harmonics inside the muffin-tin spheres with Lmax =

10, 6 and 6, respectively.

四、結果與討論

The powder XRD patterns of the Sr2FeMO6 (M

= Mo, W) samples are shown in Figure 1. Each composition of these samples is of single phase. For the samples with Sr2FeMoO6 and Sr2FeWO6 all the

peaks in each pattern can be indexed on the basis of a tetragonal (space group: I4/m) and orthorhombic unit cell (space group: Immm), respectively. Moreover, the concept of the tolerance factor can be adapted to double perovskites as well. In general, for double perovskites, with mixed A-site AA´BB´O6, the

tolerance factor (tfactor) is defined: 25,26

(1)

In which rA, rA´, rB, rB´and rOare the ionic radii

of the respective ions. The tfactor = 1 for the

compound with an ideal cubic perovskite structure. If tfactor < 1, the perovskite structure is likely to be

unstable. Therefore, the tfactor decreased (from 0.990

for Sr2FeMoO6 to 0.988 for Sr2FeWO6) while gave

rise to unstable the structure and induced structure changes from tetragonal to orthorhombic unit cell at RT. Figures 2 (a) and (b) display the observed and calculated X-ray powder diffraction profiles at 300 K of Sr2FeMO6 (M = Mo, W) samples, respectively. All

the observed peaks can be fitted with the reflection conditions of the space groups I4/m for Sr2FeMoO6

and Immm for Sr2FeWO6, respectively. The refined

occupancies of the Fe and Mo(W) sites shows that the ratios of Fe/Mo and Fe/W anti-site disorder are around 14﹪and 0.1﹪, respectively. Sánchez et al.17 proposed that the actual degree of order depends mainly on synthesis conditions. Therefore, an increase in order in Sr2FeWO6may be obtained with

increasing the synthesis temperature. The lattice parameters (a and c) and cell volume of the Sr2FeWO6 sample are significantly larger than that of

the Sr2FeMoO6 sample which is due to the radius of

the W5+ ions (0.62 Å ) is larger than that of the Mo5+ (0.61 Å ) ions.27 Furthermore, the Fe-O distances of Sr2FeWO6 (2.059 Å ) are large than those in

Sr2FeMoO6 (1.969 Å ). Additionally, W-O distance

(1.920 Å ) is shorter than those in Mo-O distance (1.973 Å ). Based on the unit cell data reported by Sánchez et al.17 The ordered sample FeO6 octahedral

is significantly larger (expanded) than MoO6

octahedral. This observation is coherent with the large ionic size of Fe3+ vs Mo5+.27 For the disordered sample the Fe-O and Mo-O bond lengths are more similar, as expected for the high degree of antisite disordering. Our results show the more disordered sample Sr2FeMoO6 (14 ﹪ anti-site disorder) have

similar Fe-O (1.969 Å )and Mo-O (1.973 Å ) bond lengths. Moreover, the more ordered sample Sr2FeWO6 (0.1﹪anti-site disorder) have significantly

larger FeO6 octahedral more than WO6 octahedral.

The results were consistent with the published results.17

The morphology of Sr2FeMO6 (M = Mo, W)

with (a) Sr2FeMoO6and (b) Sr2FeWO6 are observed

with a SEM as shown in Figure 3. Sr2FeWO6

microcrystals (1200 ℃ ) are distribution high homogeneity morn than that of Sr2FeMoO6 (1000

℃). This seems to indicate that the increasing the

synthesis temperature can help the grain growth during the sintering process. It also shows the shape and size of Sr2FeMO6 (M = Mo, W) about the range

2~3 ìm.

Figures 4 (a) and 4 (b) show a typical ED pattern and HRTEM lattice image, respectively, recorded along the [100] zone-axis direction of Sr2FeWO6. The

simulated pattern along zone axis [100] is shown in Figure 5 (c). The cell symmetry obtained by ED was identified by the observation only of h k l; h + k + l = 2 n reflections indicating I-centering of the unit cell which is consistent with the XRD refinement result.

The temperature dependence of high-field (H = 5 T) magnetization of Sr2FeMO6 (M = Mo, W) was

shown in Figure 5 (a). Magnetic measurements indicate an antiferromagnetic ordering for Sr2FeWO6

and ferromagnetic ordering for Sr2FeMoO6. Figure 5

(b) shows magnetic hysteretic curves recorded of Sr2FeMO6 (M = Mo, W) at T = 5 K. For the reason

clarity, we only display the region of 1 T ≥ H ≥-1 T. The magnetization curves measured at 5 K show no appreciable hysteresis for Sr2FeWO6. Moreover, it

also shows the hysteresis loop below 1 T for Sr2FeMoO6 in Figure 5 (b), consistent with the

ferromagnetic behavior mentioned above.

In the case of Sr2FeWO6, this corresponds to the

) 2 ( 2 2 O B B O A A r r r r r r t + + + + = ′ ′

antiferromagnetic transition (TN), and TN ~35 K

(Figure 6) in good agreement with a report of 37 K.10 As shown in Figure 6, the Curie-Weiss plot for Sr2FeWO6 gives Curie constant C = 6.08 and Weiss

temperature è = -32.6 K. The small and negative value of è suggests that although there exists both

weak ferromagnetic and antiferromagnetic

interactions at low temperature. The

antiferromagnetic interaction dominates over the weak ferromagnetic one. This point will be discussed later in detail.

Figure 7 shows the (a) zero-field cooled (ZFC) and (b) field cooled (FC) magnetic susceptibility (÷) vs. temperature of Sr2FeWO6 measured with the

applied field H =0.1, 0.5, 1, 3 and 5 T, respectively. The magnetic interactions are predominantly antiferromagnetic. At ~25 K there is a smaller feature which likely the result of a spin-reordering process on the magnetic sublattice. Furthermore, the presence of a spontaneous spin-reordering process is further emphasized by the magnetic measurement exhibited by the ZFC and FC curves; below the transition temperature (25 K), the ZFC and FC curves show large deviations. With increasing field, the transition is gradually masked. This seems to indicate that the presence of a weak ferromagnetic moment which can be ascribed to moment canting on the sublattices. Magnetic hysteresis curves obtained at 5 K are shown in Figure 6 (b) demonstrates the existence of a weak ferromagnetic response additionally indicating that the predominant character of the response is linear in field. This behavior was consistent with the published results.28,29

The transport properties of Sr2FeMO6 (M = Mo,

W) samples are illustrated in Figure 8. Both ñ(H = 0T), ñ(H = 1 T) and ñ(H = 3T) show a half-metallic behavior over the whole temperature range down to 5 K for Sr2FeMoO6 and an insulator behavior over the

whole temperature range down to around 170 K for Sr2FeWO6. Plots of magnetoresistance (MR) against

temperature for Sr2FeMO6 (M = Mo, W) are also

given in the inset of Fig. 8. The MR ratio is define by MR (T,H) = [ñ (T,H = 0) - ñ (T,H = 3 T)]/ ñ (T,H = 3 T)] where H denotes the external field. The large MR ratio of ~22﹪(H = 3 T) at room temperature (RT) was observed in the Sr2FeWO6 compound. However,

the Sr2FeMoO6 compound did not show any

significant MR even at high fields and RT (MR ~ 1﹪; H = 3 T and 300 K).

Information about the effective oxidation states of Fe and the local structural distortions around these ions is provided by X-ray absorption spectroscopic (XAS) investigations. Specifically the chemical shift of an atomic absorption edge to high energy, with increasing formal oxidation state of that atom, is the simplest and most commonly used XAS valence indicator. Figure 9 shows the Fe L2,3-edge XANES

spectra of Sr2FeMoO6 and Sr2FeWO6 along with the

FeO, Fe3O4 and Fe2O3 standards. The main spectral

features of the L2,3 edge of Fe originate from dipole

transitions from the core Fe 2p level to the empty Fe 3d states.30,31 The spectra show two broad multiplet structures separated by spin–orbit splitting of Fe 2p3/2

(L3 edge; 705 ∼ 715 eV) and Fe 2p1/2 (L2 edge; 715 ∼

725 eV). Both the edges, L3 and L2, are further

divided into two peaks. The splitting and intensity ratio between the two peaks is determined by the interplay of crystal-field effects and electronic interactions. The L3 absorption edge of Fe

II

species in an octahedral crystal field typically exhibits a main peak at a lower energy (∼708 eV), followed by a weaker peak or a shoulder at a higher energy (∼710 eV). Based on the chemical shift, both the Sr2FeMoO6 and Sr2FeWO6 of Fe valence is much

greater than 2+ but less than 3+. The average valence for Fe has also been found to be intermediate between high-spin configurations values of Fe2+ and Fe3+ from MÖssbauer spectroscopy studies.8,32

Moreover, the Fe valence of Sr2FeMoO6is slightly

lower that that of Sr2FeWO6 as compared to the

relative intensity at the energy of 708 eV and 710 eV, respectively.13 This phenomenon may be correlated to the anti-site effect of the titled compounds.

To discuss the different transport properties between the Sr2FeMO6 (M = Mo, W) samples, we

use the full-potential augmented plane-wave (FLAPW) method to do the band structure calculations. The calculations were based on the Rietveld refined models of Sr2FeMoO6with the

tetragonal unit cell and Sr2FeWO6 with the

orthorhombic unit cell. The density of states obtained by this calculation is shown in Figure 10 (a) for Sr2FeMoO6 and (b)(c)for Sr2FeWO6. The predicted

electronic features for Sr2FeMoO6 and

Sr2FeWO6resembles those calculated by Kobayashi

et al.3 and Fang et al.6 Based on the above descriptions, the fundamental question is why the W case so different from the Mo case despite the fact that W is 5d analogue of Mo in the row of the Periodic Table? Fang et al.6 proposed that the p-d hybridization between oxygen and M (Mo, W) to the main source of this different. Because the 5d orbital of W is more extended than the 4d orbital of Mo, the stronger 2p(O)-5d(W) hybridization pushes the 5d band, which is the p-d antibonding state, higher in energy. Therefore the Sr2FeWO6 band gap opens up

and the electron transfer will not occur. Our band structure calculations as shown in Figure 10 are consistent with the published results6 and show that the p-d bonding counter part in the energy position of the spin-up t2g bands is clearly deeper for Sr2FeWO6

than that of Sr2FeMoO6.

五、結論

In order to investigated the interaction among 3d(Fe)、4d(Mo) and 5d(W) orbitals of transition metal ions via oxygen ions. The crystal structure, magnetic and magnetotransport properties of B  -site transition metal Sr2FeMO6 (M = Mo, W) with double

perovskites structure have been investigated systematically. Powder X-ray diffraction analyses

revealed that Sr2FeMoO6 and Sr2FeWO6 have the

tetragonal cell (space group: I4/m) and the orthorhombic cell (space group: Immm), respectively.

The Curie-Weiss fit for Sr2FeWO6 gives Curie

constant C = 6.08 and Weiss temperature è = -32.6 K. The small and negative value of è suggests that although there exists both weak ferromagnetic and antiferromagnetic interactions at low temperature. The properties of these two compounds are summarized as follows: Sr2FeMoO6 - half-metallic

and ferromagnetic; Sr2FeWO6 - insulator and

antiferromagnetic. The changes observed by physical measurements are supported by FLAPW band structure calculations to explain the interaction between the 3d(Fe)、4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions. The p-d bonding counter part in the energy position of the spin-up t2g bands is deeper for SFWO than that of

SFMO.

六、計畫成果自評

We have reached the goals of the research plan, some part of the results have already publicized or in scientific journals [13,32,33].

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(24)[23] Larson, A. C.; Von Dreele, R.B.; Generalized

Structure Analysis System (GSAS); Los Alamos

National Laborator Report LAUR 86-748, 1994.

(24)[24] Blaha, P.; Schwarz, K.; Madsen, G. K. H.; Kvasnicka, D.; Luitz, J., WIEN2k, An

Augmented Plane Wave + Local Orbitals Program for Calculating Crystal Properties (Karlheinz Schwarz, Techn. Universitat Wien, Austria), 2001, ISBN 3-9501031-2.

[25] Galasso, F. S.; Structure, Properties and

Preparation of Perovskite-Type compounds;

Pergamon, London, 1969.

(1)[26] Westerburg, W.; Lang, O.; Ritter, C.; Felser, C.; Tremel, W.; Jakob, G. Solid State Commun. 2002,

122, 201.

[27] Shannon, R. D. Acta Crystallogr. A 1976, 32, 751. [28] Amow, G.; Greedan, J. E.; Ritter, C. J. Solid State

Chem. 1998, 141, 262.

[29] Azad, A. K.; Ivanov, S.; Eriksson, S. –G.; Rundlöf, H.; Eriksen, J.; Mathieu, R.; Svedlindh, P. J. Magn.

Magn. Mater. 2001, 237, 124.

[30] Crocombette, J. P., Pollak, M.; Jollet, F.; Thromat, N.; Gautier-Soyer, M. Phys. Rev. B 1995, 52, 3143.

[31] Gautier-Soyer, M. J. Eur. Cer. Soc. 1998, 18, 2253. [32] Woodward, P. M. Acta Crystallogr., Sect. B 1997,

53, 32.

[33] Chan, T. S.; Liu, R. S.; Guo, G. Y.; Huang, C. Y,

Int. J. Mod. Phys. B (in press).

[34] Chan, T. S.; Liu, R. S.; Guo, G. Y.; Hu, S. F.; Lin, J. G.; Chen, J. M,; Ching-Ray. Chang, Submitted

to Chem. Mater. 20 25 30 35 40 45 50 55 60 S.G : I4/m In te n si ty 2 θ Sr₂F eM oO₆ S.G : Im m m Sr2F eW O6 20 0.0 0.4 0.8 1.2 1.6 2.0 C o u n t x 1 0 5

9 Fig. 1. XRD patterns of Sr2FeMoO6 indexed in a

tetragonal unit cell (I4/m) and Sr2FeWO6 indexed in a

orthorhombic unit cell (Immm).

Fig. 2. Rietveld fits to powder XRD data of Sr2FeMO6 (M = Mo, W) with (a) Sr2FeMoO6 ; space

group I4/m and (b) Sr2FeWO6 space group Immm, at

300K. Observed (crosses) and calculated (solid line) intensities are shown with the difference at the bottom.

Fig. 3. Scanning electron micrograph of Sr2FeMO6

(M = Mo, W) with (a) Sr2FeMoO6and (b) Sr2FeWO6.

Fig. 4. (a) ED pattern and (b) HRTEM lattice image along the [100] direction of Sr2FeWO6 sample. (c)

Simulated pattern along the zone axis [100].

Fig. 5. (a) Temperature dependence of high-field (H = 5 T) magnetization of Sr2FeMO6 (M = Mo, W) (b)

The magnetization hysteresis curves (M vs. H) recorded at T =5 K of Sr2FeMO6 (M = Mo, W).

20 40 60 80 100 0.0 0.2 0.4 0.6 0.8 1.0 (a ) Sr₂F eM oO₆ I4/m C o u n t x 1 0 4 2 θ

(

b

)

(

a

)

0 50 100 150 200 250 300 350 0 4 8 12 16 20 24 _{(a )} T_N=35 K Sr₂F eM oO₆ Sr₂F eW O₆ H = 5 T M a g n e ti z a ti o n ( e m u /g ) T em p er a t u r e (K ) -1.0 -0.5 0.0 0.5 1.0 -30 -20 -10 0 10 20 30 (b ) Sr2F eW O6 Sr2F eM oO6 M a g n e ti z a ti o n ( e m u /g ) H (T esla ) 0.04 0.06 0.08 Sr₂F eW O₆ m o le /c m 3 ) 1 T 40 60 80 100 1/χ ( m o le /c m

10 Fig. 6. Magnetic susceptibility (÷) and Curie-Weiss plot for Sr2FeWO6 in the temperature from 5 K to

350 K.

Fig. 7. Magnetic susceptibility (÷) vs. temperature in (a) zero-field cooled (ZFC) and (b) field cooled (FC) of Sr2FeWO6 measured with the applied field H =0.1,

0.5, 1, 3 and 5 T.

Fig. 8. Temperature dependence of resistivity at a magnetic field of 0 T, 1 T and 3 T of Sr2FeMO6 (M =

Mo, W) with (a) Sr2FeMoO6 and (b) Sr2FeWO6. (b)

Plot of MR% against temperature of Sr2FeMO6 (M =

Mo, W) is also given in the inset.

0 50 100 150 200 250 300 350 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Z F C H = 0.1T H = 0.5T H = 1 T H = 3 T H = 5 T (a ) Sr₂F eW O₆ χ ( e m u / g - O e ) T em p er a t u r e ( K ) 0 50 100 150 200 250 300 350 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 H = 0.1T H = 0.5T H = 1 T H = 3 T H = 5 T F C (b ) Sr₂F eW O₆ χ ( e m u / g - O e ) T em p er a t u r e ( K ) 0 50 100 150 200 250 300 0.6 0.8 1.0 1.2 1.4 1.6 1.8 T em p er a t u r e (K ) (a ) Sr₂F eM oO₆ 3 T 1 T 0 T ρ (1 0 -3 o h m -c m ) 0 50 100 150 200 250 300 0 2 4 6 8 10 M R ( % ) T em p er a t u r e (K ) 0 100 200 300 400 0 2 4 6 8 10 12 14 16 ρ ( 1 0 6 o h m -c m ) 1 T 3 T 0 T (b ) Sr₂F eW O₆ T em p er a t u r e (K ) 150 200 250 300 22 24 26 28 30 32 34 36 M R ( % ) T em p er a t u r e (K ) Sr F eW O 2p_1/2→ 3d 2p_3/2→ 3d _{F e L-ed ge}

R

e

la

ti

v

it

y

A

b

s.

Fig. 9. Fe 2p-edge X-ray absorption near edge structure (XANES) spectra of Sr2FeMoO6 and

Sr2FeWO6 along with of three standards, FeO, Fe2O3

and Fe2O3

Fig. 10. The density of states (D.O.S) of (a) Sr2FeMoO6 and (b)(c) Sr2FeWO6.

(附件)

行政院國家科學委員會補助專題研究計畫

利用化學控制合成新穎電子/離子作用氧化物

及其特性分析(1/3)

出國研究心得報告

計畫編號：NSC 91－2113－M－002－044

出國期間：91 年 8 月 26 日至 91 年 8 月 28 日

出國人員：劉如熹 台灣大學化學系（計畫主持人）

中 華 民 國 九 十 二 年 六 月

會議經過:

2002 年第二次 IEEE 奈米技術會議(2002 2

nd

IEEE Conference on Nanotechnology；

IEEE NANO’ 2002)於八月二十六日至二十八日於美國華盛頓(Washungton D.C.)之希爾

頓飯店(Hilton Hotel)召開。會議由美國海軍研究所之 Clifford Lau 博士擔任一般主席

(general chair)，而由芝加哥伊利諾大學之 George Uslenghi 教授擔任議程主席(program

chair)。大會計收到約二百多篇論文，其中僅接受 190 篇之口頭(oral)論文發表，於為期

三天的議程中計涵蓋下列主題：

-Phonons in nanostr uctures and nanodevices

-Nanofabr ication, nanolithogr aphy, and growth and synthesis of nanostr uctures

-Atomic force microscopy, nano-scale manipulator s and scanning tunneling

microscopy

-Nanowire devices and applications

-Nanomagnetics

-The science and technology of nano and molecular electronics

-Nanotechnology: biological systems and applications

-Nanophotonics, optics in nanoscience, and optical diagnostics

-Nanoelectronics: MOS str uctures, molecular tr ansistor s, devices, components,

and tr anspor t

-Nanometamatrer ials

-

Nanoelectronics

-Nanocr ystalline str uctures and par ticles

-Molecule-based devices -quantum dots and forces on nanopar ticles:

applications and proper ties

-Assembly, patter ning, and manipulation on the nanoscale

patent databases and analytical tools

-Nanotubes: devices, applications, processing and assembly

-Enviromental implications of nanotechnology

-Single-electron devices and systems

議 程 中 第 二 天 下 午 安 排 一 Panel Discussion ， 題 目 為 ： Grand Challenges in

Nanoelectronics ，由各國專家先報告其對本主題之看法，再由聽眾提出問題共同討論，

此種方式於一般國際會議例屬少見，但此種雙向溝通非常有助於對主題之瞭解。於會議

中一般均同意奈米技術將由 2004 年之 90 奈米至 2016 年之 22 奈米發展之趨勢，但 2016

年後新的物理機制將被發展，而屆時亦有新的 scaling law 出現。至 2040 年單電子元件

之技術將純熟，但其必符合為一穩定、可重複與低價且量產之生產率，於其時重要關鍵

性產品將出現。一般預估未來元件與奈米電子相關產業之市場約為 6 億美元。

第二天傍晚大會安排一 Plenary talk，由普林斯頓大學之 Steven Y. Chou 教授演講，

題目為： A Grand Challenge in Nanoelectronics ，其於演講中首先闡述各種新的元件，

如 quantum effect devices、 single-electron devices、carbon nanotube devices，其並報告利

用高分子具自組裝特性並配合轉印技術而提出新的奈米製程方法，其並預估未來奈米技

術相關市場為: A trillions US Dollars Market。

於議程中值得參考之演講略述如下：

(1) 日本 NTT 公司之 Akira Fujiwara 博士報告題為：Nanotechnology Research in NTT ，

其報告該公司於矽奈米元件及奈米光晶體(photonic crystal)之發展現況，其目標由奈

米技術(nanotechnology；NT)進入量子資訊技術 (quantum information technology；

QIT)，其並指出單電子電晶體因以單電子操作，故具極低之輸入能量(ultra-low

power)，且因其非常小之體積，故具極大尺度之整合(Ultra-large scale integration)。

最近該公司已發展出 3 nm 寬度直型及 Y 型單電子電晶體，並於室溫具庫倫阻斷效

應。

(2) 日本 RIKEN 研究所之 Eiichi Maruyama 教授報告題為：Nanotechnology Research

Promotion at RIKEN ，其報告該研究所自 1980 年即發展奈米技術相關之研究，目前

正與工業界、學界及其他研究所成立整合型計畫，其乃欲發展奈米相關之生化、量

測、資訊等技術。

(3) 澳洲之澳大利亞國立大學之 C. Jagadish 教授報告題為：Nanotechnology Research in

Australia ，其報告中指出 Australian Research Council (ARC)於 2003 年計投入澳幣 1

仟 300 萬至 1 仟 500 萬元於奈米相關之研究，主要發展奈米材料。

(4) 台 灣 工 研 院 電 子 所 之 之 蔡 銘 進 博 士 報 告 題 為 ： Nanoelectronics Research at

ERSO/ITRI，其報告該研究所未來將發展單電子電晶體(與荷蘭合作)，記憶及邏輯相

關之奈米元件。

(5) 美國休士頓大學之 W. N. Hulsey III 博士報告題為：Patent Databases and Analytical

Tools for Nanotechnology Research, Design and development ，其報告自 1925 年至

1995 年專利呈指數成長之趨勢，於未來奈米技術之發展世界各先進國均投入相當之

財力，故對專利之爭取更是發展未來奈米相關之工業之決勝關鍵，其演講中亦提出

如何利用專利查詢方法瞭解目前奈米技術之發展。

(6) 美國 Rice 大學之 Vicky Colvin 教授報告題為：Nanotechnology and the Enviroment ，

其報告中指出奈米材料並非為一非活性行(inert) 材料，其進入我們生存之環境或人

體將造成某種程度之危害，故呼籲發展奈米材料雖有所助益人類對更深入技術之產

品之掌握，但亦會於此同時對其造成危害之評估亦漸形重要。

參加心得

：

奈米技術之研究衍然已成為二十一世紀全世界科研之盛事，有鑑於此 IEEE 學會舉

辦此第二次之國際性研討會，有助於全世界各國研究人員對奈米科技於電子相關技術與

元 件 發 展 概 況 之 瞭 解 。 由 會 議 中 大 家 對 奈 米 技 術 共 同 之 認 知 為 ： (1) 透 過

bottom-up/top-down 接近之共同基礎技術，(2)具整合性(interdisciplinary)與(3)影響未來新

元件與新功能產品之發展。透過對奈米技術之操控所產生之奈米結構元件將展現新機

械、熱、電子、光子及量子等特性。於會議中本人發表題為: Growth of Nano-sized Copper

Seed Layer on TiN and TaSiN by New Non-toxic Electroless Plating 之演講，此乃全世界首

度於 TaSiN 之阻障層可利用無電極電鍍之方法成功第地成長銅之晶種層，本報告得到各

國代表專家之好評，使其對我們實際於奈米半導體製程之發展有所認識，此外並與各國

專家充分交換研究心得，獲益良多，於此感謝國科會之補助。

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