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Previous issue date: 2016-12-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Lead-free multifunction composites are of great interest to the scientific community
as they have several potential applications. Such composites were produced from the ferroelectric
compound free of lead niobate and potassium sodium tantalate (KNNT) and the
magnetic nanoparticles of cobalt ferrite (CFO). A particulate composite was then produced
with the ferroelectric matrix and magnetic nanoparticles. First, the influence of the sintering
temperature (950 and 1100 °C) on the ceramic densification process was investigated.
Ceramics sintered at 950 °C showed very low density, unlike those sintered at 1100 °C, which
have a density of 90%. The microstructure of the composites and how the magnetic particles
are distributed in the matrix were investigated. The composites presented the perovskite,
spinel and tungsten bronze structural phases; The lattice constant of all crystalline phases
remained constant, so there was no migration of cations between the distinct phases. The
value of the relative dielectric constant of the pure KNNT is 700, which is comparable to
the values found in the literature. In the composites, the dielectric constant value decreases
coherently with the amount of cobalt ferrite. The coercivity of the nanoparticles before and
after the sintering is 1494 and 675 Oe, respectively, in the composites the value of coercivity
remains constant. On the other hand, the saturation magnetization of nanoparticles before
and after sintering is 63 and 68 emu/g, respectively. The value of the saturation magnetization
reduces coherently with the amount of ferrite present in the other composites. In this
way, it was shown that the electrical and magnetic properties coexist in the composite, since
the magnetic properties depend exclusively on the cobalt ferrite. / Comp´ositos multifuncionais livre de chumbo s˜ao de grande interesse na comunidade
cientif´ıca, pois possuem v´arias aplica¸c˜oes em potencial . Tais comp´ositos foram produzidos
a partir do composto ferroel´etrico livre de chumbo niobato e tantalato de s´odio e pot´assio
(KNNT) e as nano part´ıculas magn´eticas de ferrita de cobalto (CFO). Sendo ent˜ao produzido
um comp´osito particulado com a matriz ferroel´etrica e as nanopart´ıculas magn´eticas.
Primeiramente investigou-se a influˆencia da temperatura de sinteriza¸c˜ao (950 e 1100°C) no
processo de densifica¸c˜ao das cerˆamicas. As cerˆamicas sinterizadas a 950°C apresentaram
densidade muito baixas, diferentemente das sinterizadas a 1100°C que possuem densidade
de 90%. Foi investigada a microestrutura dos comp´ositos e como as part´ıculas magn´eticas
s˜ao distribu´ıdas na matriz. Os comp´ositos apresentaram as fases estruturais perovskita,
espin´elio e bronze de tungstˆenio; o parˆametro de rede de todas as fases cristalinas se mantiveram
constante, portanto n˜ao houve migra¸c˜ao de c´ations entre as fases distintas. O valor
da constante diel´etrica relativa do KNNT puro ´e 700, que ´e compar´avel aos valores encontrados
na literatura. Nos comp´ositos o valor da constante diel´etrica decresce, coerentemente,
com a quantidade de ferrita de cobalto. A coercividade das nanopart´ıculas antes e ap´os
a sinteriza¸c˜ao s˜ao 1494 e 675 Oe, respectivamente, nos comp´ositos o valor da coercividade
se mant´em constante. Por outro lado, a magnetiza¸c˜ao de satura¸c˜ao das nanopart´ıculas
antes e ap´os a sinteriza¸c˜ao s˜ao 63 e 68 emu/g, respectivamente. O valor da magnetiza¸c˜ao de
satura¸c˜ao reduz coerentemente com a quantidade de ferrita presentes nos demais comp´ositos.
Desta forma, mostrou-se que as propriedades el´etricas e magn´eticas coexistem no comp´osito,
uma vez que as propriedades magn´eticas dependem exclusivamente da ferrita de cobalto.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.bc.ufg.br:tede/6821 |
| Date | 22 December 2016 |
| Creators | Carvalho, Fernando Marques |
| Contributors | Franco Júnior, Adolfo, Franco Júnior, Adolfo, Valverde, Clodoaldo, Santana, Ricardo Costa de |
| Publisher | Universidade Federal de Goiás, Programa de Pós-graduação em Fisica (IF), UFG, Brasil, Instituto de Física - IF (RG) |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da UFG, instname:Universidade Federal de Goiás, instacron:UFG |
| Rights | http://creativecommons.org/licenses/by-nc-nd/4.0/, info:eu-repo/semantics/openAccess |
| Relation | 3162138865744262028, 600, 600, 600, 600, -4029658853652049306, 1368929812056116627, 2075167498588264571 |
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