Materials Sciences and Applications, 2013, 4, 739-745
Published Online November 2013 (http://www.scirp.org/journal/msa)
http://dx.doi.org/10.4236/msa.2013.411093
Open Access MSA
739
Phase Transition in Superconducting Thin Films of Tl
System Employing a One-Zone Furnace and Deposited by
Spray Pyrolysis
Jorge Luis Rosas-Mendoza1,2, L. Perez-Arrieta3, Miguel Aguilar-Frutis1*, Ciro Falcony4,
R. Vázquez-Arreguín1, Alejandro Miguel Rosas-Mendoza1
1Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada, Instituto Politécnico Nacional, México D.F., México; 2Unidad
Profesional Interdisciplinaria de Biotecnología, Instituto Politécnico Nacional, México D.F., México; 3Unidad Académica de Física,
Universidad Autónoma de Zacatecas (UAZ), Zacatecas, México; 4Departamento de Física, Centro de Investigación de Estudios
Avanzados (CINVESTAV-IPN), México D.F., México.
Received September 4th, 2013; revised October 16th, 2013; accepted October 30th, 2013
Copyright © 2013 Jorge Luis Rosas-Mendoza et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
A study of the phase transitions in superconducting thin films of the Thallium-Barium-Calcium-Copper (TBCCO) sys-
tem is carried out. In particular, it was got the Tl-1223 phase. For this purpose, and using the ultrasonic spray pyrolysis
technique, Barium-Calcium-Copper precursor films were first obtained. Upon deposition of the precursor films, and as
a second step, they were thallium (Tl) diffused in the one-zone furnace at 860˚C. This methodology resulted in super-
conducting films that showed a phase transition as follows: Tl-2223 → Tl-2223 + Tl-2212 → Tl-2212 → Tl-1223,
achieved between 2 and 7 hours of thallium diffusion. The evidence of the phase transitions was corroborated by the
experimental results of X-ray diffraction, energy dispersive spectroscopy and resistance-temperature measurements.
Keywords: Superconductors; Thin Films; Ultrasonic Spray Pyrolysis
1. Introduction
Recently, thin films of high Tc superconducting oxides
have attracted much attention due to their unique physi-
cal characteristics and its potential for application in the
near future. The applications of high Tc superconductors
(in thin film or bulk) are in microelectronics, in power
systems, in high current systems, in storage systems of
superconducting magnetic energy, and in others [1-6].
Among general processes for the preparation of high Tc
superconducting thin film are sputtering [7], pulsed laser
ablation [8], chemical vapor deposition, organic metal [9],
the molecular beam epitaxy [10], sol-gel [11], and others.
In general, processes for preparing superconducting thin
films by using a vacuum system maintenance are expen-
sive and complex in operation. Reports on the prepara-
tion of superconducting TBCCO system using the spray
pyrolysis technique have also been made [12,13]. The
great advantages of the process of this deposition tech-
nique include its simplicity, high deposition rate, large
storage area, controlled chemical composition and low
cost. A job of interest is the phase obtaining thallium thin
film 1223 using a single zone furnace. The Tl-1223
phase is of considerable importance because it has, on
the other phases, the highest critical current density out-
side and inside strong external magnetic fields [14].
Coupled with this, obtaining the same in most simple and
direct stages is always advisable as its synthesis in the
furnace area. The methodology involved in the two-zone
furnace includes the preparation of a precursor film and
after the addition of thallium in the latter. For this, last
step two temperatures should be considered optimal: the
precursor film and the source of thallium. Furthermore,
one should consider optimal distance between source
precursor film and thallium, since thallium gas and oxy-
gen gas must be transported along this distance to reach
the precursor film and incorporated within it thus form-
ing the superconducting phase Tl-1223 the film [15]. For
this reason, the service work is to obtain this phase in the
furnace zone, a way to avoid the inherent complexities
prevailing in the two-zone furnace. The preparation of
*Corresponding author.

Phase Transition in Superconducting Thin Films of Tl System Employing a One-Zone
Furnace and Deposited by Spray Pyrolysis
740
some bulk superconductors has already been completed
in the furnace a zone [16,17]. However, as far as it is
consulted, it has not been reported obtaining thin films of
Tl-1223 system on a one zone oven, nor undertaken a
systematic study of the superconductor(s) phase(s) in this
system (zone oven). This research paper presents results
of both the phase transition and superconducting thin
films of Tl-1223 phase TBCCO system. The supercon-
ducting films were obtained by the two-step method. The
formation of a precursor film was achieved first by ul-
trasonic spray pyrolysis, and after the diffusion of thal-
lium, as a second step, we obtained the superconducting
film. It was found that the phase transition is as follows:
Tl-2223 → Tl-2223 + Tl-2212 → Tl-2212 → Tl-1223, and
occurs between 2 and 7 hours after the start of the diffusion.
2. Experimental Details
Superconducting films were synthesized by the two step
process. In the first stage, the precursor films with stoi-
chiometry Ba2Ca2Cu3 were deposited by spray pyrolysis
ultrasonic technique using a solution of acetylacetonates
0.006 M of Ba, Ca, Cu (2, 4-pentanedionates) dissolved
in N,N-dimethylformamide (N,N-DMF). The substrates
consisted of silver plates Goodfellow (99.9%) with di-
mensions 10 mm × 5 mm, and 0.25 mm thick. These
substrates were polished mechanically with a suspension
of diamond-shaped grains with size from 1.0 m to 0.1
m. The ultrasonic spray pyrolysis system has been used
for synthesis of films. This is basically a spray tank (ob-
tained from ultrasonic pulses) of a solution made from
the source material of interest on the hot substrate. As the
carrier gas may be used air, oxygen, etc. At adequate
pressure [18]. Commercial ultrasonic humidifier operat-
ing at 750 KHz, is used in this work to generate the
aerosol solution. Additionally, air was used as carrier gas
at a flow rate of 5.0 l/min. The deposition time of the
precursor films was 60 minutes at 565˚C. The thallium
diffusion process was conducted in a single zone furnace
using a chamber consisting of a quartz tube of high pu-
rity of 61 cm long and 4 cm in diameter. The thallium
source consisted of a tablet with 0.1 grams of Tl2O3 +
0.42 grams of BaCuO2 + 0.17 grams of Ca2CuO3. The
tablet and closely precursor film were placed and en-
closed in a bag of silver, and the latter inserted into a pot
of alumina in the middle of the oven. The furnace was
brought to a temperature of 860˚C (thalliumnization tem-
perature) at a heating rate of 300˚C/h. Temperature of
860˚C was maintained for 2, 5, 6, 7 and 8 hrs and then
allowed to cool to room temperature. During the process
of diffusion of Tl, a flow of high purity oxygen (O2) was
allowed to pass at a speed of 0.5 cm3/min through the
furnace chamber. The microstructure of the films are
characterized by scanning electron microscope JEOL,
JSM-6300, equipped with an EDS system, JED-2300T to
observe the surface morphology and chemical compo-
sition estimate both precursor films and films thallinated
with thallium or broadcast. The crystalline structure of
the films was evaluated by X-ray diffraction using a
Siemens D-5000 diffractometer (Cu K
 , 0.15406 nm).
The indexing of the diffraction peaks, and the ratio of the
phases was assessed using the MATCH program [19].
The characterization of the critical temperature (Tc), was
performed with the technique of the four points, using a
constant current of 100 mA. Finally, the average rough-
ness of the superconducting films was measured with a
profilometer Veeco, Dektak3 model.
3. Results
Representative morphology obtained by SEM of the
precursor films that shown in Figure 1. The chemical
composition analysis estimates the following stoichio-
metry: Ba = 22.14% at., Ca = 29.63% at. and Cu = 48.33%
at. Based on the ideal composition of the films (30% at.
Ba, 30% at. Ca and 40% at. of Cu) we can see that these
films are rich in Cu and poor in Ba. However, previous
work has shown that this film precursor composition may
be sufficient to obtain superconducting films of Tl-1223
phase in the two-zone furnace and with high values of Tc
[20]. Both the morphology and the composition of the
precursor films are of great importance since strongly
influence the composition and characteristics of super-
conducting films final broadcast thallium [20]. Thallium
diffusion was performed on average 860˚C (858.7˚C -
860.7˚C), and duration times of 2, 5, 6, 7 and 8 hrs. After
the diffusion treatment of thallium in precursor thin
films, they were analyzed by diffraction rX, Figure 2.
Shows that after treatment of 2 hours, the sample P1
shows phase Tl-2223, which is stable because the pres-
ence of mixed phases is almost zero, the highest num-
Figure 1. Representative morphology of the precursor sam-
ples.
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Phase Transition in Superconducting Thin Films of Tl System Employing a One-Zone
Furnace and Deposited by Spray Pyrolysis
741
Figure 2. X-Ray spectra. Samples P1 phase Tl-2223, sample
BCC5 phase Tl-2223 (+)-Tl-2212 (*), sample BCC10 phase
Tl-2212, sample 1A phase Tl-1223.
ber of diffraction peaks corresponding to the Tl-2223
phase.
The phase identification was corroborated with JCPDS
card 000 411 334. Unindexed peaks are from the sub-
strate. BCC5 sample, which had a 5-hour treatment,
shows a diffractogram consistent with a mixed phase
composed of the phase Tl-2212 and Tl-2223, showing a
greater presence second phase (Tl-2223). The presence
of secondary phases is negligible. Moreover, with 6
hours of treatment observed in the diffraction pattern of
the sample BCC10 Tl-2212 phase in stable form and no
trace of Tl-2223 phase. Finally, it is observed that after 7
hours of diffusion thallium (diffractogram of sample 1A)
displays the phase of Tl-1223 almost stably and without
the presence of secondary phases. At 8 hours of treat-
ment the sample has a significant thinning it impossible
to visualize the presence of phases in the diffractogram.
The chemical composition of the samples is presented in
Table 1. The table we observe that the samples: P1 (heat
treated 2 hours and Tl-2223 phase), the sample BCC10
(6 hours treatment phase Tl-2212) and sample 1A (7-
hour treatment phase and Tl-1223) have chemical com-
positions that are similar to the theoretical composition
of each phase. Also be observed for the sample X, be-
cause it was very thin, the amount of thallium is showed
lower. The first three samples have shorter times of 8
hours, the sample which has less Tl is 1a, which shows
the phase Tl-1223 and having more amount of the sample
Table 1. Chemical composition of thallinated samples in 2, 5,
6, 7 and 8 hrs.
Chemical composition
% atomic
Sample
Time of
Thallination
(hrs) Phase Tl Ba Ca Cu
P1 2 Tl-2223 22.65 21.39 24.4231.52
BCC5 5
Tl-2223
Tl-2212 25.96 22.34 23.7827.91
BCC10 6 Tl-2212 26.90 22.40 15.2935.29
1A 7 Tl-1223 11.02 20.21 32.4236.65
X 8 - 8.64 19.23 28.0744.06
Tl-2223 22.2 22.2 22.2 33.4
Tl-2212 28.57 28.57 14.2828.57
Ideal
composition
Tl-1223 12.5 25.0 25.0 37.5
is BCC5 Tl, which has the mixed phase Tl-2223-Tl-2212.
Also observed that the diffusion time for the amount of
thallium in the samples increases gradually as the transi-
tion occurs phases: 2 hours, Tl-2223 phase (% at. of Tl =
22.65), 5 hours, phase Tl-2212-Tl-2223, (% at. of Tl =
25.96), and 6 hours Tl-2212 phase (% at. of Tl = 26.90).
However, until 7 hours, there is a reduction, Tl-1223
phase (% at. of Tl = 11.02).
The morphologies of the samples P1 (2 hours of treat-
ment) and BCC5 (5 hours of treatment), are both similar,
showing platelets not defined in shape, their borders are
seen not so marked because they have a certain cast, plus
some training appears sub-grains at the surface of BCC5.
For sample BCC10 (6 hours treatment) shows a mor-
phology with a higher melt (platelets are not seen), but
more sub-grains on the molten surface can be seen, fi-
nally the specimen A1 (Treatment 7 hours), shows plate-
let morphology with grain boundaries more marked than
those observed in the P1 and BCC5 samples. The mor-
phology of the sample with X, with 8 hours of treatment,
lost shape and observed platelet shape grains without it
seems that material has a higher level of melt relative to
those with the above samples. The R vs. T curve is
shown in Figure 3, which gave values of about 110 K
TC for sample P1, of 99 K for the sample BCC5, for
sample 96 K and 100 K for BCC10 Sample 1A corre-
sponding with those reported for these phases of the fam-
ily of thallium. Finally, Table 2 summarizes the values
of Tc obtained in this work and the values obtained by
other groups, demonstrating that the Tc values obtained
in this study are comparable to the one obtained by other
research groups. Table 2 lists values of roughness that
are present in the samples.
4. Discussion
The identification of the phases 2223, 2212 and 1223 of
the system is achieved by comparing TBCCO diffracto-
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Phase Transition in Superconducting Thin Films of Tl System Employing a One-Zone
Furnace and Deposited by Spray Pyrolysis
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Figure 3. Figure shows the electric behavior R vs T of the
samples: P1 (phase Tl-22 23 ), BCC5 (Tl-2223-Tl-2212), BCC10
(Tl-2212) and 1A (Tl-1223).
Table 2. Tc values, roughness, thallination time and phases
of the samples obtained in this work. A comparison with Tc
values obtained by other groups are shown.
Sample P1 BCC5 BCC10A1
Phase 2223
2223
2212 2212 1223
Time of diffusion of thalio
(hrs) 2 5 6 7
Tc (˚K) (this job) 110 99 96 105
Rugosity (Å) (this job) 5719 4244 6000 3435
Sugise [21] Tc (K) 115 108
Aselage [22] Tc (K) 107 104
Holstein [23] Tc (K) 106
O’Connor [24] Tc (K) 102
grams of the samples with the letters JCPDF (Tl -2223:
000 411 334, 000 420 352 Tl-1223, Tl-2212 000 391 482)
and its corresponding index is as diffractograms shown in
Figure 2. Diffractograms seem check surface geometry of
the films observed by scanning microscopy, because the
plates simulate a c-axis orientation of the crystal structure.
Certain crystalline phases are tetragonal structures,
which is in agreement with that reported in the literature,
as TBCCO superconductors exhibit this structure to-
gether with one or two Tl-O layers and layers alternating
perovskite Ba2Can+1CunO2n+1 and/or homologous series
TlmBa2Can-1CunO2n+m+2 where m = 1, n = 1 - 5 are the
phases of a single Tl-O layer and m = 2, n = 1 - 4 are
double-layer phases of Tl-O [25]. Relative to the phase
transition, it was mentioned that the volatility of thallium
oxide at temperatures of forming the superconducting
phase (close to 800˚C), is difficult to control [26]. Cer-
tain considerations between solid-vapor equilibrium be-
tween thallium oxide source and the precursor film are of
considerable importance. Oxide is known that (Tl2O) is
the only phase of thallium oxide in gaseous form [27]
and it can progress to the thallium-containing oxides
such as Tl2O3 and Tl2Ba2CaCu2O8 or used to lead to the
formation of latter. That is, this is an irreversible chemi-
cal reaction [28]. It has been mentioned that the Tl-2212
phase in bulk can be obtained from a precursor phase and
BaCuO and vapor of Tl2O and O2.
For bulk materials has been found that the formation of
compounds TBCCO proceeds via the reaction sequence as:
Tl (2201) → Tl (2212) → Tl (2223) → Tl (1223) →
Tl (1234) → Tl (1245) or Tl (2201) → Tl (2212) → Tl
(2223) → Tl (1212), [29]. In our case it is likely that af-
ter treatment of thallination 2 hours, the partial pressure
P of thallium oxide (Tl2O) and thallium diffusion into the
film has reached the optimum value to obtain Tl-2223
phase in the P1 film whose composition is very close to
ideal, see Table 1. The proximity of the precursor sample
and the constant value of the oxygen partial pressure P
(O2), could lead to vapor control thallium oxide (Tl2O)
during treatment and dissemination. Furthermore, the
morphology of the film is presented feature of this phase
(molten in certain platelet-shaped grains).
The % at. thallium, as determined by EDS in sample
BCC5 indicates the presence of a larger number average
thallium (25.96% at.), considering the combination of the
phases Tl-2223 + Tl-2212 . In our case, greater incorpo-
ration of thallium could have been accomplished with
increased thallination time. The morphology of the sam-
ple does not change much compared BCC5 sample P1,
except perhaps to the increased presence of subgrains on
platelets. It seems that the nature of the sub-grains attrib-
utable to the onset of the second phase superconduc-
ting Tl-2212, as seen in the morphology of the sample
BCC10, which has as such sub-grains are filled to a
greater extent the sample, probably the Tl-2212 phase.
For the latter film thallium concentration was of the order
of 26.90% at., a value closest to the ideal concentration
for the Tl-2212 phase.
Finally at 7 hours of thallination occurs a decrease in
the amount of thallium present in the film (to a value of
11.02 % at.), Resulting in phase Tl-1223. Regarding
morphology reappear platelet-shaped grains, again simu-
lating the c axis orientation. After passing the period of 7
hours thallination by EDS shows that the stoichiometry
of the films begins to degrade, losing large amounts of
thallium, probably by an erosion of the superconducting
film. Figure 4(e) (Sample X), illustrates how the mor-
phology of the film is degraded. The process seems then
be one in which the precursor film goes into the super-
conductor at some stage during thallination with thallium,
but also involves a degradation of the film, which be-
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Phase Transition in Superconducting Thin Films of Tl System Employing a One-Zone
Furnace and Deposited by Spray Pyrolysis
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743
(a) (b)
(c) (d)
(e)
Figure 4. (a) The figure shows different morphologies that are presented in a thalinated films: 2 h (Figure 4(a) shows P1), 5 h
(Figure 4(b) shows BCC5), 6 h (Figure 4(c) shows BCC10), 7 h (Figure 4(d), Sample 1A) and 8 h (Figure 4(e), Sample X), re-
spectively; (b) The figure shows morphology for 5 h, sample BCC5; (c) The figure shows the morphology for 7 h, sample
BCC10; (d) The figure shows the morphology of 7 h, Sample 1A; (e) The figure shows the morphology for 8 h, Sample X.
comes visible after 7 hours of thallination, probably be-
cause of the presence of thallium or thallium vapors
along with the flow of oxygen is supplied at all times of
the thallination. Measurements of R vs T seem also rein-
force that no correspondence with the phases present,
according to their values of Tc we have of the materials
in bulk: Tl-2212 (90 - 110 K), Tl-2223 (118 - 125 K) and
Tl-1223 (100 - 110 K).

Phase Transition in Superconducting Thin Films of Tl System Employing a One-Zone
Furnace and Deposited by Spray Pyrolysis
744
From the results of composition, microscopy, diffrac-
tion and temperature-resistance, seems to occur to obtain
superconducting films has the following phase transfor-
mation route: Tl-2223 → Tl-2223 + Tl-2212 → Tl-2212
→ Tl-1223, with the 7-hour period to achieve optimal
phase of thallium 1223. Manufacturing routes involving
superconducting thin films on one side closed crucible
method [29] and on the other, the process in the two-zone
furnace [30]. Using the first method and how far we have
consulted, the research does not show a phase transition
route, only mention under what conditions it is possible
to achieve the crystalline phase Tl-2212 [31] or Tl-2223
phase [32], most of these studies agree to use thallium
diffusion temperatures between 750 and 800˚C and gas
atmospheres such as Ar, O2 or air. Using the second
method, there have been several studies on crystalline
phase growth superconducting thin films of Tl [33], these
studies have shown that in this system there may be ire-
versible phase transition and Tl-2223 and Tl-2212 [34].
This research showed that the deposition technique ul-
trasonic spray pyrolysis can be a viable technique for the
growth of superconducting thin films is also available
from superconducting thin films phase Tl-2223, Tl-2212
and Tl-1223 stably by the two-step method, using a one
zone furnace.
5. Conclusion
By spray pyrolysis, deposition technique ultrasonic test
predicts the feasibility of obtaining superconducting thin
films with phases: Tl-2223, Tl-2212, and Tl-1223 stably
by two-step method with the use of an oven area. It was
found that the diffusion of thallium and the presence of
oxygen flow is the one most likely limiting the appear-
ance of most of these phases following the transition path
as Tl-2223 → Tl-2223 + Tl-2212 → Tl-2212 → Tl-1223.
6. Acknowledgements
This research was made possible thanks to the research
assistants, Marcela Guerrero, Ana Bertha Soto, Zachary
Rivera from the Dept. of Physics at CINVESTAV-IPN
and Alfonso Martinez from CICATA-IPN.
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Furnace and Deposited by Spray Pyrolysis
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