Bottom-up and top-down approaches to the synthesis of 2D gadolinium-doped cerium oxide (CGO) at low temperature
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2018
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INTERNATIONAL CONGRESS ON CERAMICS, 7th; CONGRESSO BRASILEIRO DE CERÂMICA, 62.
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In the last decades, 2D nanosheets have been studied for their physicochemical
properties, which are different from the bulk of the original material or any other
nanostructure, therefore a challenging and exciting area of nanomaterial synthesis.
Nanosheets can be used in the production of low cost electro-optics, stable highperformance
batteries, high performance catalysts, etc. In general, there are two main
approaches in the synthesis of nanomaterials: top-down and bottom-up. A top-down
approach starts from a macroscopic material, which undergoes exfoliation or grinding
to reduce its size to a nanometric scale. However, this type of process induces defects,
compromising its properties. In the bottom-up method the nanostructures are built
molecule by molecule, resulting in a more homogenous and controlled material.
In this work, 2D nanostructures of gadolinium-doped cerium oxide (CGO) were
synthesized by two simple and reproducible routes; both by aqueous precipitation
induced by the hydrolysis of hexamethylenetetramine. The CGO materials synthesized
were characterized by their composition, morphology and crystallographic
characteristics. The combined experimental results indicated that different
morphologies of 2D CGO can be obtained by controlling the synthesis parameters.
The temperature of the reaction medium was decisive in the formation of a more
homogeneous structure, establishing the optimum temperature to 10 ºC for the
synthesis of nanosheets. The method of liquid exfoliation, with a solution of
ethanol:water in an ultrasonic bath, was also established to obtain a suspension of
nanosheets. Comparing the microscopic images of the materials synthesized by the
top-down and bottom-up methods, it can be observed that the latter favours the
formation of a more homogeneous nanostructure, leading to the obtention of exfoliated
nanosheets with a shorter reaction and ultrasonic exfoliation time.
Lead-based ceramics are widely used piezoelectric materials due to their excellent
piezoelectric properties, but they are not environmentally friendly due to lead oxide
toxicity. [1] Therefore, a number of studies have been carried out to improve electrical
properties of different kind of ABO3 perovskites. [2] In the (1-x)K0.5Na0.5NbO3-
xBaTiO3 system the effect of (K,Na) substitution by Ba decreases the temperature of
the maximum dielectric permittivity and improves the dielectric properties.
Consequently, this kind of materials can be used as an alternative candidate to replace
conventional piezoelectric materials [3]. In this work, we present the synthesis and
characterization of (1-x)K0.5Na0.5NbO3–xBaTiO3, (x= 0.03, 0.04, 0.05, 0.06,
0.07) based lead-free piezoelectric ceramics through the solid-state reaction route.
Powders were mixed in different compositions with the final propose of obtaining
extensive applications.
It was observed that Ba2+ ions occupy the A sites of the perovskite structure, while
Ti4+ ions replace Nb5+ ions at the B sites, resulting in the distortion of the perovskite
structure. Additionally, for the highest BaTiO3 concentration a practically constant
dielectric constant curve was registered from 20 to 500°C, whereas the loss tangent
values ??were low. Lead-based perovskites are widely used for actuators, sensors and transducers due
to their excellent piezoelectric properties. However, the toxicity of lead for the
environment and human health led to focus research efforts on finding substitutes for
these materials. One candidate is the Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 solid solution, due to
its interesting properties attributed to the presence of a morphotropic phase boundary
in the composition Bi0.5(Na0.8K0.2)0.5TiO3. It is known, that the synthesis methods of
nanopowders, such as the sol-gel process, allow the control of grain size better that
other methods. Consequently, this work focuses on the study of processing conditions
and final properties of Bi0.5(Na0.8K0.2)0.5TiO3-based ceramics obtained by the sol-gel
method.
To obtain the desired phase, the reagents used were sodium acetate (CH3COONa),
potassium acetate (CH3COOK), bismuth nitrate (Bi(NO3)3·5H2O) and
titanium isopropoxide (Ti(OiPr)4). The acetates and nitrate were dissolved, separately,
in glacial acetic acid. Titanium isopropoxide was dissolved in a solution of isopropanol
and acetic acid. Acetates and nitrates were added dropwise. The mixture was stirred
for one hour. Then, it was dried at 150 °C for 2 hours, and heat-treated at different
temperatures (550 to 750 °C). The obtained powders were pressed uniaxially and
sintered in the temperature range of 1000
Como referenciar
MORAES, L.P.R.; MARANI, D.; MACHADO, M.F.S.; RODRIGUES, L.N.; FONSECA, F.C.; ESPOSITO, V.; SUN, Z. Bottom-up and top-down approaches to the synthesis of 2D gadolinium-doped cerium oxide (CGO) at low temperature. In: INTERNATIONAL CONGRESS ON CERAMICS, 7th; CONGRESSO BRASILEIRO DE CERÂMICA, 62., June 17-21, 2018, Foz do Iguaçu, PR. Abstract... p. 543-544. Disponível em: http://repositorio.ipen.br/handle/123456789/29697. Acesso em: 28 Mar 2025.
Esta referência é gerada automaticamente de acordo com as normas do estilo IPEN/SP (ABNT NBR 6023) e recomenda-se uma verificação final e ajustes caso necessário.