Deposition of Pb1-xCuxS1-δ substitutional solid solutions from aqueous solutions

Article abstract of DOI:10.1023/A:1020021704243

Thin films of Pb_1-xCu_xS_1-δ metastable substitutional solid solutions containing up to 3.5 mol % Cu ₂S were deposited from aqueous solutions and characterized by physicochemical methods.

Full text of DOI:10.1023/A:1020021704243

Inorganic Materials, Vol. 38, No. 9, 2002, pp. 870–872. Translated from Neorganicheskie Materialy, Vol. 38, No. 9, 2002, pp. 1037–1040.
Original Russian Text Copyright © 2002 by Maskaeva, Markov, Ivanov.
Deposition of Pb Cu S Substitutional Solid Solutions
d
x 1 –
1 – x
from Aqueous Solutions
L. N. Maskaeva, V. F. Markov, and P. N. Ivanov
Ural State Technical University, ul. Mira 19, Yekaterinburg, 620002 Russia
e-mail: mln@ural.ru
Received September 5, 2001; in final form, January 30, 2002
Abstract—Thin films of Pb1 – xCuxS1 − δ metastable substitutional solid solutions containing up to 3.5 mol %
Cu2S were deposited from aqueous solutions and characterized by physicochemical methods.
Metal sulfides find wide industrial application. In for lead ions, and ammonia served as both an alkali and
particular, thin metal sulfide films are employed as a ligand for copper ions. These complexing agents were
optoelectronic materials, conducting coatings, and sor- selected because their complexes with lead and copper
bents. Of special interest are copper sulfides, which
possess a variety of valuable properties and are used in
transparent conducting coatings for heated watch win-
dows, antistatic coatings, luminescent capacitors, flexi-
ble transparent conducting polymeric films, conducting
paper, and heat reflectors. Furthermore, they are prom-
ising sensor and photoelectric materials. From the
viewpoint of photoelectric applications, of great inter-
est are PbS–Cu2S substitutional solid solutions, which
are similar to the mineral murdochite [1]. As found by
electron probe microanalysis, natural galenite may con-
tain 4.5 to 11.5 mol % Cu (metastable solid solution)
[2]. However, according to phase-diagram data, the sol-
ubility of PbS in Cu2S at 1000 K is no greater than
1 mol % and the solubility of Cu2S in PbS is much
lower [3]. It is, therefore, interesting to obtain films of
Pb1 – xCuxS1 − δ solid solutions and study their pro-
perties.
are relatively stable: pKPb(OH)C H O3– = 13.72 [5],
6
5
7
pKCu(NH )+ = 5.93 [6], and pKCu(NH )+ = 10.86 [6].
3
3
2
To locate the composition region of PbS and Cu2S
coprecipitation, we considered the ionic equilibria in the
reaction system in the temperature range 293–353 K at
thiourea concentrations much higher than the initial
metal concentrations (C0) [7]. The purpose of our anal-
ysis was to determine the initial conditions for the for-
mation of the constituent sulfides (the ionic products
[Pb2+][S2–] and [Cu+][S2–] equal to the solubility prod-
ucts of PbS and Cu2S, respectively). The Pb2+ and Cu+
concentrations were determined by considering the
ionic equilibria in the system, and the S2– concentration
was calculated under the assumption that the hydrolytic
decomposition of thiourea into hydrogen sulfide and
cyanamide is reversible. The hydrolysis constant of
thiourea was determined earlier [7].
One promising way of preparing substitutional solid
solutions is coprecipitation from aqueous solutions.
This method is capable of extending the range of avail-
able materials through the formation of relatively sta-
ble, supersaturated solid solutions whose compositions
fall far beyond the equilibrium stoichiometry range. It
enables low-temperature deposition of films onto vari-
ously shaped surfaces.
At 348 K, PbS and Cu2S coprecipitation is possible
above pH 7 (Fig. 1). Under these conditions, the forma-
tion of metal cyanamides is ruled out. At pH 10–12,
Pb(OH)2 formation is possible. Raising pH to above 12
may cause the formation of Cu2O. The calculation
results were used to determine the component concen-
trations ensuring PbS and Cu2S coprecipitation.
Synthesis is commonly conducted in a bath contain-
ing appropriate metal salts, an alkali, complexing
agents, and a thioamide. Sulfide formation is a hetero-
geneous autocatalytic reaction. The composition of the
resulting solid solution is governed by the relative for-
mation rates of the constituent binary sulfides [4].
Films were deposited onto degreased glass-ceramic
substrates. The deposition time was 15 to 60 min,
depending on the initial concentrations of the metal
salts. The films were lustrous, adhered well to the sub-
strate, and ranged in thickness from 0.3 to 1.0 µm.
Their color varied from gray to red-brown, depending
on the copper content.
We synthesized Pb1 − xCuxS1 − δ solid solutions from
a mixture containing lead(II) acetate, copper(II) sulfate,
sodium citrate, ammonium hydroxide, thiourea as a
The films were characterized by x-ray diffraction
sulfur source, and hydroxylamine for reducing Cu(II) (XRD), energy dispersive x-ray microanalysis, electron
to Cu(I). Sodium citrate served as a complexing agent diffraction, and Raman spectroscopy.
0020-1685/02/3809-0870$27.00 © 2002 MAIK “Nauka/Interperiodica”

DEPOSITION OF Pb1 – xCuxS1 – δ SUBSTITUTIONAL SOLID SOLUTIONS
mol % Cu2S
871
pC0
9
8
7
6
4
1
1
2
3
5
4
2
2
3
3
2
1
0
1
0
4
3
7
8
9
10
11
12
13
14
0.005
0.010
0.015
0.020
0.025
pH
[Cu+], mol/l
Fig. 1. (1) PbS, (2) Cu S, (3) Pb(OH) , and (4) Cu O for-
2
2
2
mation curves and the region of PbS and Cu S coprecipita-
Fig. 2. Cu S content of the Pb
Cu S
solid solution
2
2
1 – x
x
1 − δ
tion (shaded) from
a
reaction mixture containing
as a function of the Cu concentration in the reaction mixture
at initial Pb(CH COO) concentrations of (1) 0.01, (2) 0.02,
Na C H O (0.05 mol/l), NH OH (5 mol/l), and (NH ) CS
3
6
5
7
4
2 2
3
2
(0.3 mol/l).
and (3) 0.04 mol/l. The deposition time is 60 min.
eters of cubic PbS (0.5936 nm) [10] and pseudocubic
Cu1.8S (0.556 nm) [11].
Elemental analysis was performed on a JCXA-773c
microanalyzer equipped with anAN 10/85S energy dis-
persive spectrometer. The copper(I) sulfide films had
the composition Cu1.75S. The lead sulfide films con-
tained 0.3–0.5% excess Pb, in agreement with the Pb−S
phase diagram [3]. The Cu content of the PbS–Cu2S
films was up to 9.4 at. %, depending on synthetic con-
ditions. The only crystalline phase detected in those
films by XRD had the rock-salt structure. Its unit-cell
parameter decreased with increasing Cu concentration
in the reaction mixture. These data point to the forma-
tion of Pb1 – xCuxS1 − δ solid solutions through partial
According to XRD data, the Cu2S content of the
solid solution as a function of the CuSO4 concentration
in the reaction mixture passes through a maximum
(Fig. 2). (Similar behavior was observed earlier in the
Pb1 – x CdxS solid-solution system [12].) The maximum
Cu2S content of the solid solution rises as the initial
concentration of the lead salt is lowered. At an initial
lead salt concentration of 10–2 mol/l, the highest Cu2S
content of Pb1 – xCuxS1 − δ was 3.5 ± 0.2 mol %. As fol-
lows from the PbS–Cu2S phase diagram, this solid solu-
tion is metastable. Supersaturation was also observed in
the deposition of Pb1 − xCdxS substitutional solid solu-
tions from aqueous media [4, 12].
substitution of Cu+ (r = 0.096 nm) for Pb2+ (r =
0.132 nm) [8].
Raising the Cu concentration in the starting solution
was found to increase the amorphous content of the
films. This was confirmed by scanning electron micros-
copy (JEOL JUS-5900 LV instrument). The PbS films
consisted of polyhedral grains, typically 0.2 to 0.7 µm
in size. Even small CuSO4 additions (<10–4 mol/l)
caused dramatic changes in the morphology of the
(100) surface and led to the formation of misshapen,
poorly faceted grains. Raising the CuSO4 concentration
The formation of substitutional solid solutions in the
PbS–Cu2S system is corroborated by the polarized
Raman spectra of the deposits (Renishaw-1000 spec-
trophotometer, Ar+ laser, λ = 514.5 nm). Cu2S gives a
characteristic Raman band at 472 cm–1 [13] (Fig. 3). As
the CuSO4 concentration in the starting solution is
to above 10–3 mol/l decreased the predominant grain
size down to 0.05 µm and caused further microstruc-
tural changes: we observed first rounded and then cres-
cent aggregates, the latter being characteristic of Cu2S
films.
Cu2S
Cu0.026Pb0.974
S
Cu0.018Pb0.982
S
The XRD patterns of the films were obtained on a
DRON-3 diffractometer (CuKα radiation). The compo-
sition of the solid solutions was determined using Veg-
ard’s law. For most dilute sulfide solid solutions, the
deviation from Vegard’s law is within the experimental
error (about 10–4 nm) [9]. The percentage of Cu2S in the
solid solutions was evaluated using the unit-cell param-
PbS
1000
800
600
400
200
0
Wavenumber, cm–1
Fig. 3. Raman spectra of Pb
Cu S
films.
1 – x
x
1 − δ
INORGANIC MATERIALS Vol. 38 No. 9 2002

872
MASKAEVA et al.
raised, the band due to PbS shifts from 133 to 141 cm–1,
indicating that Pb is partially replaced by Cu, a lower Z
element. Raising the copper content of the solid solu-
tion increases the background intensity. Note that the
spectra exhibit bands assignable to lead hydroxide
(955 cm–1) [14]. Our Raman scattering data for PbS–
Cu2S thin films correlate with earlier results [13] for
films of metal sulfides and their solid solutions.
ductor Materials Research: A Handbook), Moscow:
Nauka, 1991, p. 252.
4. Kitaev, G.A., Markov, V.F., Maskaeva, L.N., et al., Syn-
thesis and Properties of CdxPb1 – xS Solid Solutions, Izv.
Akad. Nauk SSSR, Neorg. Mater., 1990, vol. 26, no. 2,
pp. 248–250.
5. Tikhonov, A.S., Study of Lead Complexes with Citric
Acid at Different pH Values, Tr. Voronezh. Gos. Univ.,
Sb. Rabot Khim. Fakul’t., 1958, vol. 59, pp. 79–94.
6. Lur’e, Yu.Yu., Spravochnik po analiticheskoi khimii
(Handbook of Analytical Chemistry), Moscow:
Khimiya, 1971.
7. Kitaev, G.A., Bol’shchikova, T.P., Fofanov, G.M., et al.,
Thermodynamic Analysis of Conditions for Metal Sul-
fide Precipitation with Thiourea in Aqueous Media, in
Kinetika i mekhanizm obrazovaniya tverdoi fazy (Kinet-
ics and Mechanisms of the Formation of Solid Phases),
Sverdlovsk: Ural. Polytekh. Inst., 1968, no. 170,
pp. 113–126.
CONCLUSION
Metastable
substitutional
solid
solutions
Pb1 − xCuxS1 − δ (0 < x < 0.035) were synthesized for the
first time by PbS and Cu2S coprecipitation from thio-
urea-containing aqueous solutions.
The phase composition of the precipitates and
deposited films was determined, and the effect of the
CuSO4 concentration in the starting solution on the film
morphology was studied.
8. Urusov, V.S., Energeticheskaya kristallokhimiya (Ener-
getic Crystal Chemistry), Moscow: Nauka, 1975.
The Cu2S content of Pb1 – xCuxS1 − δ was found to
depend in a complex way on the composition of the
reaction mixture.
9. Chichagov, A.V. and Sipavina, L.V., Parametry yacheek
tverdykh rastvorov (Lattice Parameters of Solid Solu-
tions), Moscow: Nauka, 1982.
10. Bethke, P.M. and Barton, P.B., Subsolidus Relations in
the System PbS–CdS, Am. Mineral., 1971, vol. 56,
pp. 2034–2039.
ACKNOWLEDGMENTS
11. Chopra, K. and Das, S., Thin Film Solar Cells, New
York: Plenum, 1983. Translated under the title Tonkople-
nochnye solnechnye elementy, Moscow: Mir, 1986,
p. 177.
12. Markov, V.F., Maskaeva, L.N., and Kitaev, G.A., Predict-
ing the Composition of CdxPb1 – xS Films Deposited
from Aqueous Solutions, Neorg. Mater., 2000, vol. 36,
no. 12, pp. 1421–1423 [Inorg. Mater. (Engl. Transl.),
vol. 36, no. 12, pp. 1194–1196].
13. Minceva-Sukarova, B., Njdoski, M., and Chnnilall, C.J.,
Raman Spectra of Thin Films of Metal Sulfides, J. Mol.
Struct., 1997, vol. 410/411, pp. 267–270.
14. Nakamoto, K., Infrared and Raman Spectra of Inorganic
and Coordination Compounds, Chichester: Wiley, 1986.
Translated under the title IK-spektry i spektry KR neor-
ganicheskikh i koordinatsionnykh soedinenii, Moscow:
Mir, 1991, p. 256.
This work was supported by the US Civilian
Research and Development Foundation (grant
no. REC-005) and the Russian Foundation for Basic
Research (R-2001-Ural, grant no. 01-03-96518).
REFERENCES
1. Povarennykh, A.S., Factors Governing the Isomorphism
of Elements, Mineral. Sb. L’vov. Gos. Univ., 1964,
vol. 18, no. 2, pp. 126–144.
2. Craig, J.R. and Kullerud, G., Phase Relations and Min-
eral Assemblages in Copper–Lead–Sulfur System, Am.
Mineral., 1968, vol. 53, no. 1/2, pp. 145–161.
3. Shelimova, L.E., Tomashik, V.N., and Gritsiv, V.I., Dia-
grammy sostoyaniya v poluprovodnikovom materia-
lovedenii: Spravochnik (Phase Diagrams in Semicon-
INORGANIC MATERIALS Vol. 38 No. 9 2002