SYNTHESIS, STRUCTURE, AND PROPERTIES OF SOLID SOLUTIONS
569
Powders
Bi(RCOO)
3
Fe O
2
3
(1 – x)BiFeO × x[Pb(Zr/Ti)]O
3
3
x = 0.1
Zirconium Titanium
+
+
precursor
precursor
Ln
Pb(RCOO)
2
Iron
(1 – x)BiFeO × x[(Pb
Ln )(Zr/Ti)]O
y 3
3
(1 – y)
M(AcAc)
n
precursor
precursor
x = 0.1, y = 0.1
–
Ti(n = 2, 2Cl ); Zr(n = 4)
Bismuth
Lead
+
+
+
precursor precursor
Ln(RCOO) × mH O
Zr/Ti = 0.65/0.35, 0.53/0.47
Ln = La, Pr, Gd, Yb
3
2
Fig. 1. Scheme for making solid solutions based on bismuth ferrite.
while [Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.65Ti0.35)0.1]O3 and tions depended on their synthesis method. The solid-
phase synthesis has a drawback in that it is difficult to
obtain single-phase materials both before and during
calcination. In recent years, both inorganic and organic
derivatives have been widely used as the initial com-
pounds. They solve an important problem of a uniform
distribution of components in the charge and, hence, the
complex oxide material.
[Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.53Ti0.47)0.1]O3 (Ln = La, Pr,
Gd,Yb) solid solutions were prepared by the method of
modified solid-phase synthesis, which consisted in the
use of powdered reagents, such as mixtures of metal
oxides with organic and inorganic salts. The charge
contained the initial components in an amount suffi-
cient for obtaining a cation stoichiometric mixture,
which was calcined at temperatures from room temper-
ature to 600–750°ë in Nabertherm furnaces at a heating
rate of 2°C/min; the holding time was 2 h.
X-ray phase analysis. The structure, the parame-
ters, and the phase composition of the samples at inter-
mediate synthesis stages were determined according to
results of the X-ray phase analysis performed by the
powder method with ionization registration of diffrac-
tion maxima using a DRON-3 apparatus (CuKα radia-
tion, λ = 0.1540 nm, 2θ = 18°–60°, the step ∆2θ = 0.05°).
Additional measurements were performed over a nar-
row interval of angles 2θ = 38°–41° at a step ∆2θ = 0.02°
so as to determine the type of perovskite structure dis-
tortion and calculate the lattice parameters.
The synthesis conditions and the sintering tempera-
tures of the [Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.65Ti0.35)0.1]O3
(L = La, Pr, Gd, Yb) solid solutions were chosen on the
basis of earlier results of thermogravimetric analysis of
synthesized BiFeé3, since bismuth ferrite is the main
component of the solid solutions under study. The use
of the modified solid-phase synthesis allowed the for-
mation temperature of the solid solutions at hand to be
reduced to 600°ë.
The diffraction patterns of the samples of
[Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.65Ti0.35)0.1]O3
and
[Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.53Ti0.47)0.1]O3 (Ln = La, Pr,
Gd, Yb), which were annealed at 600°ë, confirmed the
formation of perovskite, but included traces of
Bi36Fe2O57 and Bi2Fe4O9 impurity phases.
Morphology of the ceramic. Specific features of
the surface morphology of the ceramic were studied in
the contact mode of a SOLVER-PRO47 atomic force
microscope (NT MDT) with a cantilever made of NSG
10/20 crystal silicon.
The unit cell parameters for the compositions under
study are given in the table. All the compounds retained
a typical “perovskite” structure with hexagonal distor-
tion. The volume of the crystal lattice of the
[Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.65Ti0.35)0.1]O3 solid solu-
tions under study changed. The crystal lattice decreased
upon addition of La, but increased with respect to the
[Bi0.9Pb0.1][Fe0.9(Zr0.65Ti0.35)0.1]O3 solid solution as Pr,
Gd, and Yb were added. The crystal lattice of
Magnetic measurements. The magnetic character-
istics of the solid solutions were measured on a Quan-
tum Design SQUID magnetometer in different mag-
1
netic fields at temperatures of 5–700 K.
[Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.53Ti0.47)0.1]O3
increased
RESULTS AND DISCUSSION
monotonically upon addition of La, Pr and Gd, but
Bi1 – xPbxFe1 – xZrxO3 solid solutions (x = 0.1–0.2) and
increased
sharply
with
respect
to
the
previously
unstudied
[Bi0.9Pb0.1][Fe0.9(Zr0.53Ti0.47)0.1]O3 solid solution upon
[[Bi0.9(Pb0.9Ln0.1)0.1][Fe0.9(Zr0.65Ti0.35)0.1]O3 solid solu-
tions (L = La, Pr, Gd,Yb) were prepared as shown in the
scheme in Fig. 1. This scheme was used to synthesize a
group of solid solutions based on bismuth ferrite with
addition of 10–20% PbZrO3 and 10% LZT or
Ln-alloyed LZT. The analysis of some studies [8, 9]
suggested that the physical properties of the solid solu-
alloying with Yb.
The
microstructures
of
the
undoped
and
[Bi0.9Pb0.1][Fe0.9(Zr0.53Ti0.47)0.1]O3
[Bi0.9Pb0.1][Fe0.9(Zr0.65Ti0.35)0.1]O3 are shown in Fig. 2.
It is seen from the microphotographs that the morphol-
ogy of the ceramic changed little with the molar ratio of
Zr and Ti ions. Oriented scaly crystals with a lateral
dimension of 0.5 to 1 µm, which grew as mutually par-
allel layers, were observed in both cases. Furthermore,
1
The magnetic measurements were performed at the Angstrom
Laboratory, Uppsala University, Sweden.
INORGANIC MATERIALS Vol. 45 No. 5 2009