Abstract In the present research, the synthesis of cobalt oxide Co3O4 was carried out using the sol-gel technique with subsequent heat treatment at 225 and 235 °C. The final product obtained was characterized by X-ray diffraction (XRD), showing a pure crystalline phase of Co3O4, cell parameters a=b=c=8.071 Å, and a volume of 525.7 Å3. The particle size was between 2.37 and 2.77 µm, which indicated that structural transformations from Co to Co3O4 induced an increase in the particle size. Through Rietveld refinement, the interatomic distances and inclination angles of the Co1, Co2, and Co3 polyhedra were analyzed in order to establish the structural behavior of cobalt oxide (II, III) at 235 °C. The UV-vis analysis allowed determining band gap (Eg) with values of 1.6 eV in the first region and 0.97 eV in the second. Scanning electron microscopy images showed that the particles agglomerated with increasing calcination temperature and exhibited larger particles. This work presents a detailed analysis of structural parameters of Co3O4 using the Vesta software with Rietveld refinement data.

A transição de fase estrutural de ferroelétrico para paraelétrico foi estudada por espalhamento Raman em cerâmicas de titanato de chumbo (PbTiO3) dopadas com lantânio (La). O modo vibracional A1 contém alguns picos que tem sido associados na literatura com a concentração de PbTiO3 (Ca, Ba), e os efeitos das altas temperaturas ao se aproximar da temperatura de Curie (Tc). Um novo estudo Raman mostra que o comportamento anômalo do modo A1 não é apenas causado pelos efeitos da concentração ou da temperatura próxima de Tc, mas por anarmonicidade e defeitos na rede do PbTiO3 são termodinamicamente inevitáveis. Este efeito foi estudado em uma ampla faixa de temperatura de 10 K a Tc em cada amostra (La = 0, 5, 10, 15, 20%), mostrando que o efeito depende não somente das altas temperaturas no PT puro.

The structural phase transition from ferroelectric to paraelectric was studied by Raman scattering in the ceramic lead titanate (PbTiO3) doped with lanthanum (La). A1 vibrational mode contains some sub-peaks that have been associated in literature with PbTiO3 concentration (Ca, Ba), and effects of high temperatures as it approaches the Curie temperature (Tc). Raman new study shows that the anomalous behavior of the A1 mode is not only caused by the effects of concentration or temperature near Tc, but by anharmonicity and defects in the network in the PbTiO3 thermodynamically are inevitable. This effect was studied by a wide temperature range from 10 K to Tc in each sample (La = 0, 5, 10, 15, 20%), showing that the effect depends not only on the high temperatures in the pure PT.