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Growth of epitaxial TlBaCaCuO a-axis oriented films on LaAlO3 buffer layers grown on SrTiO3 (100) substrates
,, ,,
,,,
Journal of
AILLOY5 AND COMPOUHDS ELSEVIER
Journal of Alloys and Compounds 251 (1997) 314-317
Growth of epitaxial TIBaCaCuO a-axis oriented films on LaA10 3 buffer layers grown on SrTiO 3 ( 1 0 0 ) substrates G. Malandrino, A. Frassica, G.G. Condorelli, G. Lanza, I.L. Fragal/l* Dip. Scienze Chimiche. Univ. Catania. V.le A. Doria 6. 95125 Catania. Italy
~.~tract
a-Axi~ t~riented films of the TIBaCaCuO family have been grown on LaAIO~ (100) buffer layers on SrTiO~ (I00) substrates. The two ~c¢p fabrication procedure involves the deposition of BaCaCuO(F) matrices through metal-organic chemical vapour deposition (MOCVD) and their annealing to yield the TIBaCaCuO phase through a thallium vapour diffusion process. The present unusual orientation, which to our knowledge is the first example of an a-axis orientation for this class of superconductors, is due to the nature of the LaAIO~ buffer layers deposited on SrTiO~ (l(~) substrates, The LaAIO~ films deposited in-situ via MOCVD from the new generation precursor La(hfa)~.diglyme (hfa= l, I. 1,5,5,5=hexafluoro.2,4.pentanedione, diglyme = bis(2-methoxyethyl)ether) and Al(acac)~ (acac = acetylacetone) are highly (100) oriented. The lull widths at half maximum (F3,VFIM) of the rocking curve of the (IO0) peak as small as 0.16° have been observed. Kevword~: Buffer I~ycrs; MOCVD; Thallium vapour diffusion
|, Introduction Films of superconducting TIBaCaCuO phases are of interest for their potential applications in microclectronic devices. In the last t~w year~, many efforts have been made to fabricate reproducible, single phase thin films, and many interesting results have been reached either in terms of processing conditions of the TIBaCaCuO phases (I ~41 or in terms of new phases produced [2,5,6f However, all the data available to date, whatever the fabrication technique, synthetic strategy and substrates have been used, univocally point to the tbrmation of c-axis oriented TIBaCaCuO thin films. On the other hand, a great interest has been devoted to the synthesis of films with the :'°axis parallel to the substrate, i.e.. aoaxis oriented fires or (110) oriented films. In fact. different film orientations may be needed in view of particular applications such as tunnel and Josephson junctions since it is well known that the su~rcondueting coherence lengths of YBaCuO and BiS~aCuO su~rcono duelers along the c.axis are one order of magnitude smaller than those along the a-axis. To date, a°axis oriented YBaCuO superconducting thin films have been prepared by several methods [7~9l, while ~'C~:)tte~nding author. Tel: (39o95) 33b-578: Fax: (39,95) :~80.138; e-maih fragala@ictuniv,uaict,it 0925~8388/97/$17.~ © 1997 Elsevier Science S,A, All rights re~rved PII S0925-8388~95~02693,X
only a few studies on the fabrications of thin iilms without coaxis orientation have been reported for the BiSrCaCuO family I I0,111. In particular, aoaxis oriented BiSrCaCuO tilms have been deposited by magnetron sputtering It01 and by M ~ V D on (100) MgO substrates 111]. To our knowledge, there are no reports on the t~brications of TIBaCaCuO thin tilms with the a-axis orientation. In this paper we report on the fabrication of a-axis oriented TIBaCaCuO films through a combined MOCVD and thallium vapour diffusion approach on LaAIO~ (IO0) buffer layers grown by MOCVD on SrTiO~ (lO0) substrates.
2, Experimental The conditions of fabrication of LaAIOt (100) buffer layer on SrTiO:~ (I00) substrate will be reported elsewhere [12]. The BaCaCuO(F) matrices were deposited from Se "second generation" metal-organic complexes Ba(hfa) 2. tetraglyme, Ca(hfa):,tetraglyme prepared as reported elseo where [ 13]. Cu(acac)z purchased from Aldrich was purified by sublimation. Depositions were carried out in a low pressure, horizontal, cold wall reactor with a resistive suhstrate heater [ 14]. The flow-rates of the carder gas (AO and the sublimation temperatures of the three precursors were individually fixed to control the film stoichiometry.
315
G. Malandrino et al. I Journal of Alloys and Compounds 251 (1997) 314-317
Pure oxygen was used as the reactant gas and introdu::ed into the reactor through a separate line. Mass flows were controlled with ! 160 MKS flowmeters using an MKS 147 electronic control unit ( _ 1 sccm accuracy). Depositions were carded out at 7 ton" total pressure. Each precursor was maintained at constant temperature in the 85-140 °(2 range and the substrate was l'~eated at 450-500 °(2. The LaAIO a (100)lSrTiO 3 (100) substrates were used directly as produced from the MOCVD deposition, without any further treatment. The random oriented YSZ substrates, cut from YSZ single crystals without any particular alignment, were used after sonication in ethanol. An open reactor was used for the thallium vapour diffusion step. The as-deposited films containing fluoride phases [6] were directly annealed in a covered crucible in the presence of an oxide mixture of I.STI,O3:2BaO:lCaO:2CuO (I.5:2:1:2) stoichiometry as source of the volatile thallium oxide, at 900 °C for 5 min under a pure oxygen flow. The chemical composition of the films was analysed by energy dispersive X-ray analysis (EDX) and the surface morphology was examined by scanning electron microscopy (SEM). The thickness of the films after the thallium vapour diffusion step was about I-1.5 p~m. 0-20 X-ray diffraction (XRD) patterns were recorded on a computer interfaced Philips PW 1130 powder diffractometer using a Ni-filtered CuKa radiation, operating at 40 kV/20 mA over a 40<20<80 ° angular range. The full width at half maxiraum ( l ~ H M ) of the (100) reflection at 22.80° of a single crystal SrTiO.~ substrate is 0.11 °.
3. Results and discussion
3. I. LaAIO, btql~l~Jrlayers on SrTiO, (100) substmw
xmwr~c'uo~uuao~ smo A
ii ._;.
0
10
20
in,
30
40
SO
6O
70
gO
z 0 (degrees) Fig. !. 0-20 X-ray diffraction pattern of an MOCVD-derived a-axis oriented TIBaCaCuO film on LaAIO~ (IO0)lSrTiO~ (!00) substrates.
(00,12) reflection of the c-axis oriented domains of the 2212 phase. At present it is not possible to determine the superconducting phase of the a-axis oriented domains from the 0-20 scan since the lattice constants of the a-axis are very similar for all the TIBaCaCuO superconducting phases. The SEM image of the TIBaCaCuO phase film on LaAIO 3 (100)lSrTiO 3 (100) is reported in Fig. 2. Note the long and narrow grains of the superconducting phase that intersect to each other at right angles. The EDX analyses of the single grains indicate a 2.1:2.5:1.0:2.1 stoichiometry. A control experiment was, therefore, designed using a typical BaCaCuO(F) film on a YSZ substrate, simuhano eously annealed with a BaCaCuO(F) matrix on a LaAIO~/ SrTiO~ substrate. The film grown on the YSZ substrate shows only the usual c.axis orientation, with the domains
LaAIO~ buffer layers have been grown on SrTiO:~ (100) substrates using MOCVD from the new generation precursor La(hfa)~.diglyme ll5l and Al(acac)~. The X-ray diffraction pattern shows only (h00) reflections (considering a pseudocubic structure) [161 thus indicating a 100 orientation. The 0 rocking curve of the 100 peak has a full width at half maximum (FWHM) ranging from 0.16 ° to 0.69 ° 1121.
3.2, Preparation ~ TIBaCaCuO phases SrTiO~
on
LaAIOJ
The TIBaCaCuO films were prepared by a two step process: (i) deposition of a BaCaCuO(F) matrices and (ii) ex-situ anneal in a thallium environment. The annealing was carried out at 900 °C for 5 min in the presence of a 1.5:2:1:2 oxide mixture. The X-ray diffraction pattern is reported in Fig. !. Note that only the h00 peaks of the TIBaCaCuO phases are present in addition to a very low intensity peak at 36.8 °, which can be associated with the
Fig. 2. $EM image of an MOCVD'derived aoaxls oriented TIBaCaCuO lilm on LaAIO~ ( 100)/SrTiO~ (100) substrates. The right-hand side is tl~ area within the white rectangular box magnified 3 times.
G. Malandrino et al. 1 Journal t~' Alho's trod Conq~ounds 251 (1997)314-317
316
Fig, 3. SEM image of an MOCVD.derived c-axis oriented 2212 film on YSZ substrate simultaneously annealed with the film repotted in Figs. I and 2.
oriented with the c-axes perpendicular to the substrate. The SEM micrograph unequivocally shows the typical platelike structures of c-axis oriented TIBaeaCuO films (Fig. 3). The diffraction pattern, reported in Fig. 4 shows only (001) reflections of the TI,BazCaCu~O , (2212) phase ; .dicating that the film has only c-axis oriented domains. The overall dam clearly point to a unique, recognisable cause for the formation of a-axis oriented domains, namely the nature of the LaAIO,~ buffer layer. It is well known that the LaAIO~ (100) substrates [3.41 as well as all the other ~ubstrates so far used (MgO (100) l l7l, S~iO~ (100) [17], NdGaO~ (I I0) l lTI) always give rise to coaxis oriented films. Even when randomly oriented YSZ substrates are used, the TIBaCaCuO films are coaxis oriented 161. It, therefore, transpires that, in the pre~nt temperature range. the nature of the LaAIO~ buffer layer determine~ the ibrmation of the aoa~is oriented films. Further inveso
tigations will be, however, worthwhile in order to study the effects of the temperature as well as of the reaction atmosphere on the orientation of TIBaCaCuO phases on LaAIO 3 (100)/SrTiO 3 (100) substrates [ 18]. Previous studies have shown that the combined effects due to the temperature, the reaction atmosphere and the stoichiometry of the oxide mixture play a crucial role on the different nature of the TIBaCaCuO phases on YSZ substrates [6]. In all cases, however, the c-axis orientation has always been found. In contrast with the aforementioned TIBaCaCuO systems, growth temperature plays a key role in the domain orientation of YBaCuO and BiSrCaCuO phases, a-Axis and c-axis oriented films may be obtained upon changing the temperature and, in particular, lower deposition temperatures favour a-axis oriented films, while c-axis oriented films form under higher temperatures. These data might be related to the in situ deposition methodology adopted for mentioned YBaCuO and BiSrCaCuO films. The different surface energies of the nuclei might thus favour the formation of different oriented domains,
4. Conclusions a-Axis oriented TIBaCaCuO superconducting thin films have been obtained on LaAIO~ (100)/SrTiO~ (100) substrates. The substrate nature seems to be uniquely responsible for the formation of this particularly oriented films. To our knowledge, this represents the first example of aoaxis oriented films among TIBaCaCuO phases.
Acknowledgments
The authors gratefully thank the Consiglio Nazionale delle Ricerehe (CNR. Rome, Pmgetto Strategico Materiali Innovativi) for financial support.
2212
References III P.C. Michael. L.G Johans~m, L. Bengtsson, T. Claeson. Z.G. lvanov. E. Olsson. P. Berastcgui and E. Stepantsov, Ph.vsica C. 235 (1994) 717. 121 G.G. Condorelli. i.L. Fragal~, G. Malandrino, F. Miletto GranotJo and M. Vale~l;ino. in E Vincent.lni (ed.), Advances in Sciences ,:ul 7'echnology ,~'. Siq~et~'tmducliviey and Suiwrconducting Materials Techmdogies. TECHNA Srl. 199~. p. 579. 13l N. Re~hauer. U, Spreitt.er. W. Brozio, A. Piehler, K.F. Renk, K. Bet get and (3. Saemannol~;henko, Appt. Phys. l~tt., 6g (1996)
<
| m
0
t0
20
30
40
~
60
70
80
20 (d~rt~} Fig. 4~ 0~20 Xotay diffraction pattern of an M~VD°derived (,-axis ~iented 2212 film on YSZ substrate simultaneously annealed with the film repotted in Figs. I and 2.
141 B.J,
Hinds. D,L, Schulz. D.A. Neumayer, B, Han. T,J, Marks, Y.Y. Wang, V.P. Dravid, J.L. Schindler, T.P. Hogan and C.R. Kannewurl: AppL Fhys. Ixtr.. 65 (1994) 231. lSI W.L Holstein, L.A. Parisi, C.R. Fincher and P.L. Gal. Physica C, 212 (1993) IlO. 161 G, Mahmdrino, G,G, CondoreUi, i.L. Fragalii, F. Miletto Granozio,
G. Malandrino et al. I Journal of AUoys alld Compmmds 251 ~1~17~ 314-317
[7] [8] [9l
[lO[
U. Scotti di Uccio and M. Valentino, Supercond. Sci. Technol., 9 ( 19961 570. Y. Gao, G. Bai, DJ. Lain and K.L Merkle, Physica C, 173 (19911 487. C.B, Eom, A.F. Marshall, S.S. Laderman, R.D. Jacowitz and T.H. Gebaile, Science, 249 (1990) 1549. A. Andreone, A. Di Chiaea, F. Miletto Granozio, U. Scotti di Uccio, M. Valentino, G,G. Condorelli, I.L Fragal'~ and G. Malandrino, in P. Vincenzini (ed,), Advances b~ Sciences and Technology 8. Superconductivity and Superconductblg Materials Technologies, TECHNA Srl, 1995, p. 165, H. Hattori, H. Itozaki and S. Yazu, Advances in Superconductivity Ill, Proc. 3rd h~t. Syrup. Superconductivi 0" (ISS'901, 1990, Sendai, p. 1050.
317
I I I I T. Sugimoto, M. Nakagawa, Y. Shiohara and S. Tanaka, Physica C, 192 (1992) 108. 1121 G. Malandrino and l.L Fragal.~, manuscript in preparation. [131 G. Malandrino, F. Casteili and I.L Fragal~, Inorg. Chim. Acta, 224 ( 19941 203. ll41 G. Malandrino, PhD Thesis, University of Catania, lla!y. 1994. G.G. Condorelli, G. Malandrino and l.L Fragal~, Chem. Mater., 6 ( 19941 1861. [15] G. Malandrino, R. Licata, F. Castelli, I.L Fragal~ and C. Benelli, h~org, Chem., 34 (1995) 6233. [16] S. Geller and V.B. Bala, Acta Co'st., 9 (19561 1019. [17] W.L Holstein, L.A. Parisi, R.B. Flippen and D.G. Swarlzfager. J. Mater. Res., 8 (19931 962. l lSI G. Malandrino arid I.L. Fragal~, manuscript in preparation.
,,,
Journal of
AILLOY5 AND COMPOUHDS ELSEVIER
Journal of Alloys and Compounds 251 (1997) 314-317
Growth of epitaxial TIBaCaCuO a-axis oriented films on LaA10 3 buffer layers grown on SrTiO 3 ( 1 0 0 ) substrates G. Malandrino, A. Frassica, G.G. Condorelli, G. Lanza, I.L. Fragal/l* Dip. Scienze Chimiche. Univ. Catania. V.le A. Doria 6. 95125 Catania. Italy
~.~tract
a-Axi~ t~riented films of the TIBaCaCuO family have been grown on LaAIO~ (100) buffer layers on SrTiO~ (I00) substrates. The two ~c¢p fabrication procedure involves the deposition of BaCaCuO(F) matrices through metal-organic chemical vapour deposition (MOCVD) and their annealing to yield the TIBaCaCuO phase through a thallium vapour diffusion process. The present unusual orientation, which to our knowledge is the first example of an a-axis orientation for this class of superconductors, is due to the nature of the LaAIO~ buffer layers deposited on SrTiO~ (l(~) substrates, The LaAIO~ films deposited in-situ via MOCVD from the new generation precursor La(hfa)~.diglyme (hfa= l, I. 1,5,5,5=hexafluoro.2,4.pentanedione, diglyme = bis(2-methoxyethyl)ether) and Al(acac)~ (acac = acetylacetone) are highly (100) oriented. The lull widths at half maximum (F3,VFIM) of the rocking curve of the (IO0) peak as small as 0.16° have been observed. Kevword~: Buffer I~ycrs; MOCVD; Thallium vapour diffusion
|, Introduction Films of superconducting TIBaCaCuO phases are of interest for their potential applications in microclectronic devices. In the last t~w year~, many efforts have been made to fabricate reproducible, single phase thin films, and many interesting results have been reached either in terms of processing conditions of the TIBaCaCuO phases (I ~41 or in terms of new phases produced [2,5,6f However, all the data available to date, whatever the fabrication technique, synthetic strategy and substrates have been used, univocally point to the tbrmation of c-axis oriented TIBaCaCuO thin films. On the other hand, a great interest has been devoted to the synthesis of films with the :'°axis parallel to the substrate, i.e.. aoaxis oriented fires or (110) oriented films. In fact. different film orientations may be needed in view of particular applications such as tunnel and Josephson junctions since it is well known that the su~rcondueting coherence lengths of YBaCuO and BiS~aCuO su~rcono duelers along the c.axis are one order of magnitude smaller than those along the a-axis. To date, a°axis oriented YBaCuO superconducting thin films have been prepared by several methods [7~9l, while ~'C~:)tte~nding author. Tel: (39o95) 33b-578: Fax: (39,95) :~80.138; e-maih fragala@ictuniv,uaict,it 0925~8388/97/$17.~ © 1997 Elsevier Science S,A, All rights re~rved PII S0925-8388~95~02693,X
only a few studies on the fabrications of thin iilms without coaxis orientation have been reported for the BiSrCaCuO family I I0,111. In particular, aoaxis oriented BiSrCaCuO tilms have been deposited by magnetron sputtering It01 and by M ~ V D on (100) MgO substrates 111]. To our knowledge, there are no reports on the t~brications of TIBaCaCuO thin tilms with the a-axis orientation. In this paper we report on the fabrication of a-axis oriented TIBaCaCuO films through a combined MOCVD and thallium vapour diffusion approach on LaAIO~ (IO0) buffer layers grown by MOCVD on SrTiO~ (lO0) substrates.
2, Experimental The conditions of fabrication of LaAIOt (100) buffer layer on SrTiO:~ (I00) substrate will be reported elsewhere [12]. The BaCaCuO(F) matrices were deposited from Se "second generation" metal-organic complexes Ba(hfa) 2. tetraglyme, Ca(hfa):,tetraglyme prepared as reported elseo where [ 13]. Cu(acac)z purchased from Aldrich was purified by sublimation. Depositions were carried out in a low pressure, horizontal, cold wall reactor with a resistive suhstrate heater [ 14]. The flow-rates of the carder gas (AO and the sublimation temperatures of the three precursors were individually fixed to control the film stoichiometry.
315
G. Malandrino et al. I Journal of Alloys and Compounds 251 (1997) 314-317
Pure oxygen was used as the reactant gas and introdu::ed into the reactor through a separate line. Mass flows were controlled with ! 160 MKS flowmeters using an MKS 147 electronic control unit ( _ 1 sccm accuracy). Depositions were carded out at 7 ton" total pressure. Each precursor was maintained at constant temperature in the 85-140 °(2 range and the substrate was l'~eated at 450-500 °(2. The LaAIO a (100)lSrTiO 3 (100) substrates were used directly as produced from the MOCVD deposition, without any further treatment. The random oriented YSZ substrates, cut from YSZ single crystals without any particular alignment, were used after sonication in ethanol. An open reactor was used for the thallium vapour diffusion step. The as-deposited films containing fluoride phases [6] were directly annealed in a covered crucible in the presence of an oxide mixture of I.STI,O3:2BaO:lCaO:2CuO (I.5:2:1:2) stoichiometry as source of the volatile thallium oxide, at 900 °C for 5 min under a pure oxygen flow. The chemical composition of the films was analysed by energy dispersive X-ray analysis (EDX) and the surface morphology was examined by scanning electron microscopy (SEM). The thickness of the films after the thallium vapour diffusion step was about I-1.5 p~m. 0-20 X-ray diffraction (XRD) patterns were recorded on a computer interfaced Philips PW 1130 powder diffractometer using a Ni-filtered CuKa radiation, operating at 40 kV/20 mA over a 40<20<80 ° angular range. The full width at half maxiraum ( l ~ H M ) of the (100) reflection at 22.80° of a single crystal SrTiO.~ substrate is 0.11 °.
3. Results and discussion
3. I. LaAIO, btql~l~Jrlayers on SrTiO, (100) substmw
xmwr~c'uo~uuao~ smo A
ii ._;.
0
10
20
in,
30
40
SO
6O
70
gO
z 0 (degrees) Fig. !. 0-20 X-ray diffraction pattern of an MOCVD-derived a-axis oriented TIBaCaCuO film on LaAIO~ (IO0)lSrTiO~ (!00) substrates.
(00,12) reflection of the c-axis oriented domains of the 2212 phase. At present it is not possible to determine the superconducting phase of the a-axis oriented domains from the 0-20 scan since the lattice constants of the a-axis are very similar for all the TIBaCaCuO superconducting phases. The SEM image of the TIBaCaCuO phase film on LaAIO 3 (100)lSrTiO 3 (100) is reported in Fig. 2. Note the long and narrow grains of the superconducting phase that intersect to each other at right angles. The EDX analyses of the single grains indicate a 2.1:2.5:1.0:2.1 stoichiometry. A control experiment was, therefore, designed using a typical BaCaCuO(F) film on a YSZ substrate, simuhano eously annealed with a BaCaCuO(F) matrix on a LaAIO~/ SrTiO~ substrate. The film grown on the YSZ substrate shows only the usual c.axis orientation, with the domains
LaAIO~ buffer layers have been grown on SrTiO:~ (100) substrates using MOCVD from the new generation precursor La(hfa)~.diglyme ll5l and Al(acac)~. The X-ray diffraction pattern shows only (h00) reflections (considering a pseudocubic structure) [161 thus indicating a 100 orientation. The 0 rocking curve of the 100 peak has a full width at half maximum (FWHM) ranging from 0.16 ° to 0.69 ° 1121.
3.2, Preparation ~ TIBaCaCuO phases SrTiO~
on
LaAIOJ
The TIBaCaCuO films were prepared by a two step process: (i) deposition of a BaCaCuO(F) matrices and (ii) ex-situ anneal in a thallium environment. The annealing was carried out at 900 °C for 5 min in the presence of a 1.5:2:1:2 oxide mixture. The X-ray diffraction pattern is reported in Fig. !. Note that only the h00 peaks of the TIBaCaCuO phases are present in addition to a very low intensity peak at 36.8 °, which can be associated with the
Fig. 2. $EM image of an MOCVD'derived aoaxls oriented TIBaCaCuO lilm on LaAIO~ ( 100)/SrTiO~ (100) substrates. The right-hand side is tl~ area within the white rectangular box magnified 3 times.
G. Malandrino et al. 1 Journal t~' Alho's trod Conq~ounds 251 (1997)314-317
316
Fig, 3. SEM image of an MOCVD.derived c-axis oriented 2212 film on YSZ substrate simultaneously annealed with the film repotted in Figs. I and 2.
oriented with the c-axes perpendicular to the substrate. The SEM micrograph unequivocally shows the typical platelike structures of c-axis oriented TIBaeaCuO films (Fig. 3). The diffraction pattern, reported in Fig. 4 shows only (001) reflections of the TI,BazCaCu~O , (2212) phase ; .dicating that the film has only c-axis oriented domains. The overall dam clearly point to a unique, recognisable cause for the formation of a-axis oriented domains, namely the nature of the LaAIO,~ buffer layer. It is well known that the LaAIO~ (100) substrates [3.41 as well as all the other ~ubstrates so far used (MgO (100) l l7l, S~iO~ (100) [17], NdGaO~ (I I0) l lTI) always give rise to coaxis oriented films. Even when randomly oriented YSZ substrates are used, the TIBaCaCuO films are coaxis oriented 161. It, therefore, transpires that, in the pre~nt temperature range. the nature of the LaAIO~ buffer layer determine~ the ibrmation of the aoa~is oriented films. Further inveso
tigations will be, however, worthwhile in order to study the effects of the temperature as well as of the reaction atmosphere on the orientation of TIBaCaCuO phases on LaAIO 3 (100)/SrTiO 3 (100) substrates [ 18]. Previous studies have shown that the combined effects due to the temperature, the reaction atmosphere and the stoichiometry of the oxide mixture play a crucial role on the different nature of the TIBaCaCuO phases on YSZ substrates [6]. In all cases, however, the c-axis orientation has always been found. In contrast with the aforementioned TIBaCaCuO systems, growth temperature plays a key role in the domain orientation of YBaCuO and BiSrCaCuO phases, a-Axis and c-axis oriented films may be obtained upon changing the temperature and, in particular, lower deposition temperatures favour a-axis oriented films, while c-axis oriented films form under higher temperatures. These data might be related to the in situ deposition methodology adopted for mentioned YBaCuO and BiSrCaCuO films. The different surface energies of the nuclei might thus favour the formation of different oriented domains,
4. Conclusions a-Axis oriented TIBaCaCuO superconducting thin films have been obtained on LaAIO~ (100)/SrTiO~ (100) substrates. The substrate nature seems to be uniquely responsible for the formation of this particularly oriented films. To our knowledge, this represents the first example of aoaxis oriented films among TIBaCaCuO phases.
Acknowledgments
The authors gratefully thank the Consiglio Nazionale delle Ricerehe (CNR. Rome, Pmgetto Strategico Materiali Innovativi) for financial support.
2212
References III P.C. Michael. L.G Johans~m, L. Bengtsson, T. Claeson. Z.G. lvanov. E. Olsson. P. Berastcgui and E. Stepantsov, Ph.vsica C. 235 (1994) 717. 121 G.G. Condorelli. i.L. Fragal~, G. Malandrino, F. Miletto GranotJo and M. Vale~l;ino. in E Vincent.lni (ed.), Advances in Sciences ,:ul 7'echnology ,~'. Siq~et~'tmducliviey and Suiwrconducting Materials Techmdogies. TECHNA Srl. 199~. p. 579. 13l N. Re~hauer. U, Spreitt.er. W. Brozio, A. Piehler, K.F. Renk, K. Bet get and (3. Saemannol~;henko, Appt. Phys. l~tt., 6g (1996)
<
| m
0
t0
20
30
40
~
60
70
80
20 (d~rt~} Fig. 4~ 0~20 Xotay diffraction pattern of an M~VD°derived (,-axis ~iented 2212 film on YSZ substrate simultaneously annealed with the film repotted in Figs. I and 2.
141 B.J,
Hinds. D,L, Schulz. D.A. Neumayer, B, Han. T,J, Marks, Y.Y. Wang, V.P. Dravid, J.L. Schindler, T.P. Hogan and C.R. Kannewurl: AppL Fhys. Ixtr.. 65 (1994) 231. lSI W.L Holstein, L.A. Parisi, C.R. Fincher and P.L. Gal. Physica C, 212 (1993) IlO. 161 G, Mahmdrino, G,G, CondoreUi, i.L. Fragalii, F. Miletto Granozio,
G. Malandrino et al. I Journal of AUoys alld Compmmds 251 ~1~17~ 314-317
[7] [8] [9l
[lO[
U. Scotti di Uccio and M. Valentino, Supercond. Sci. Technol., 9 ( 19961 570. Y. Gao, G. Bai, DJ. Lain and K.L Merkle, Physica C, 173 (19911 487. C.B, Eom, A.F. Marshall, S.S. Laderman, R.D. Jacowitz and T.H. Gebaile, Science, 249 (1990) 1549. A. Andreone, A. Di Chiaea, F. Miletto Granozio, U. Scotti di Uccio, M. Valentino, G,G. Condorelli, I.L Fragal'~ and G. Malandrino, in P. Vincenzini (ed,), Advances b~ Sciences and Technology 8. Superconductivity and Superconductblg Materials Technologies, TECHNA Srl, 1995, p. 165, H. Hattori, H. Itozaki and S. Yazu, Advances in Superconductivity Ill, Proc. 3rd h~t. Syrup. Superconductivi 0" (ISS'901, 1990, Sendai, p. 1050.
317
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