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benzene (300 ml). The mixture was refluxed for 3 h, At each temperature, the firing time was 2 h. The heat-
and then two-thirds of the benzene was distilled off. treated powders were ground and pressed at 10 MPa
The resultant orange-red precipitate was filtered off, into 10-mm-diameter pellets. The final firing step was
washed with petroleum ether, and vacuum-dried to a performed at 750°ë for 3 h.
constant weight. Quantitative yield was achieved, and
the softening temperature was 230°ë [10].
Thermal analysis[ of the powders was carried out
using the sample holder of a Netzsch STA-409 system.
Synthesis of the rare-earth acetates (general pro-
cedure). To a 500-ml four-neck flask fitted with a reflux
condenser, dropping funnel, and stirrer were added a rare-
earth (lanthanum, praseodymium, gadolinium, or ytter-
bium) oxide (0.159 mol), glacial acetic acid (250 ml), and
water (40 ml). The reaction was stirred while heating to
80–90°ë until complete dissolution of the rare-earth
oxide. After all of the rare-earth oxide was dissolved in
acetic acid, the reaction mixture was cooled, and the
rare-earth acetate was collected on a filter. The filtrate
was boiled down to near dryness in a rotary evaporator,
and the rare-earth acetate thus obtained was added to
the precipitate. Next, the rare-earth acetate was washed
with hexane, filtered off, and dried, first on the filter and
then under a dynamic vacuum of 1 Pa for 3 h (to remove
the residual acetic acid).
The samples were heated from 290 to 1020 K at a rate
of 10 K/min in air.
IR spectra were measured on a Specord M82 spec-
trophotometer in the range 600–4000 cm–1 after each
firing step, using KBr pellets.
X-ray diffraction (XRD) studies were performed
on a DRON-3 diffractometer with CuKα radiation.
XRD patterns were collected in step-scan mode
between 10° and 100°. The phases present were identi-
fied using ICDD PDF-4 data.
Surface morphology of ceramics. The surface
morphology of ceramics was examined by contact
mode atomic force microscopy (AFM) on an NT MDT
SOLVER-PRO47, using an NSG 10/20 crystalline sili-
con cantilever probe.
The Ln(CH3COO)3 · xH2O acetates (ı = 3 for La,
ı = 0 for Pr, ı = 3 for Gd, and ı = 4 for Yb) were iso-
lated with a 70 to 80% yield. Their compositions were
checked by chelatometric titration [11].
Synthesis of Pb(ZrxTi1 – x)O3 solid solutions. The
Pb(Zr0.53Ti0.47)O3 and Pb(Zr0.65Ti0.35)O3 solid solutions
were synthesized from reagent-grade lead carbonate,
PbCO3; pure-grade zirconium acetylacetonate decahy-
drate, Zr(C5H7O2)4 · 10H2O; and titanium dichlorodi-
acetylacetonate, Ti(C5H7O2)2Cl2. To more rapidly pulver-
ize and homogenize the raw materials, these were ground
in the agate mortar of a Retsch micromill at 40 rpm for
12 min.
RESULTS AND DISCUSSION
The
(Pb1 – xLnx)(Zr0.53Ti0.47)O3
and
(Pb1 − xLnx)(Zr0.65Ti0.35)O3 (x = 0.02, 0.06; Ln = La, Pr,
Gd, Yb) solid solutions were prepared by modified
solid-state synthesis using inorganic and organic metal
derivatives as precursors. Carboxylates and some other
organic metal derivatives are attractive precursors
owing to their good solubility and the ability to form
homogeneous mixtures and decompose at relatively
low temperatures without metal volatilization or release
of toxic substances. These requirements are met by zir-
conium acetylacetonate and lead acetate. Modified
solid-state synthesis included the use of various powder
reagents: metal oxide mixtures and organic and inor-
ganic salts. Mechanical activation made it possible to
enhance the reactivity of the starting reagents owing to
the water of crystallization.
Synthesis of the Pb0.98Ln0.02(Zr0.53Ti0.47)O3 + d
,
Pb0.98Ln0.02(Zr0.65Ti0.35)O3+d, Pb0.94Ln0.06(Zr0.53Ti0.47)O3+ d
,
Pb0.94Ln0.06(Zr0.65Ti0.35)O3+ d (Ln = La, Pr, Gd, Yb) solid
solutions. The solid solutions were prepared by a modified
solid-state technique. The starting chemicals used were
reagent-grade lead carbonate, PbCO3, or reagent-grade lead
acetate, Pb(CH3COO)3 · 3H2O, and presynthesized zirco-
nium acetylacetonate, Zr(C5H7O2)4 · 10H2O; titanium
dichlorodiacetylacetonate, Ti(C5H7O2)2Cl2; lanthanum(III)
acetate, La(CH3COO)3 · 3H2O; pure-grade praseodymium
acetate, Pr(CH3COO)3; pure-grade gadolinium(III) acetate,
Gd(CH3COO)3 · 3H2O; and pure-grade ytterbium acetate,
Yb(CH3COO)3 · 4H2O.
The initial stage of thermolysis in the range 70–
180°ë was represented by endothermic peaks due to
dehydration and decarboxylation processes and also to
the formation of intermediate carbonates, which decom-
posed above 500°ë. Heating led to structure breakdown,
which was caused by both the dehydration of metal-
hydroxide groups (above 200–250°ë) and the decomposi-
tion of carboxylates and other inorganic derivatives. These
processes follow a complex mechanism, with active
release of ëé2, ëé, ëç4, ë2ç6, and other gaseous spe-
cies in the range 300–470°ë. Endothermic peaks with no
weight loss are due to the crystallization of an oxide phase
from the amorphous matrix formed through the decompo-
Appropriate starting mixtures were ground into fine
powder in a Retsch micromill. The powders were fired
in Nabertherm furnaces in several steps. The first step
was performed at temperatures from 180 to 250°ë.
Next, the powders were fired in the range 400–650°C. sition of the starting mixture.
INORGANIC MATERIALS Vol. 45 No. 3 2009