Communication—Function-Oriented Design of 3D Carbon Networks Toward Negative Permittivity at kHz Frequencies

Three-dimensional (3D) carbon networks composed of graphene (GR) and carbon nanotube (CNT) were constructed in copper calcium titanate (CCTO) in order to realize negative permittivity behavior. The results show that negative permittivity can be obtained at kHz frequencies above percolation threshold when 3D carbon networks are successfully constructed. Negative permittivity originates from the low-frequency plasmonic state which is explained by the Drude model. The magnitude of negative permittivity was tuned between 105 and 106 which significantly correlates with concentration of free carriers. Moreover, the reactance spectra clarify the inductive character of negative permittivity materials.

Fabrication of lithium niobate fork grating by laser-writing-induced selective chemical etching

We propose and experimentally demonstrate a laser-writing-induced selective chemical etching (LWISCE) technique for effective micro-fabrication of lithium niobate (LN) crystal. Laser writing of LN crystal produces negative domains and domain walls. Also, it causes local lattice defects, in which the etching rates are significantly increased in comparison to the original LN crystal. In experiment, we use the LWISCE technique to fabricate various fork gratings in an X-cut LN crystal for the generation of vortex beams. In comparison to etching an untreated X-cut LN crystal, the etching rates of the laser-writing-induced boundaries and the central laser-irradiated areas are enhanced by a factor of 26 and 16, respectively. The width and depth of fork grating structure can be precisely controlled by laser writing parameters. Our method provides an efficient mask-free micro-fabrication technique for LN crystal, which can be readily applied to other ferroelectric crystals such as lithium tantalate, potassium titanyl phosphate and barium calcium titanate.

Quantification of Calcium Titanate (CaTiO3) by the Rietvield Method in Different Molar Proportions, from the Rutile Ore

O objetivo do presente estudo é produzir titanato de cálcio (CT) com estrutura perovskita (ABO3) a partir do minério rutilo e carbonato de cálcio comercial. As matériasprimas foram caracterizados por fluorescência de raios-X e difração de raios-X (XRD). Diferentes composições foram formuladas, as amostras foram comprimidas a 150 MPa e sinterizadas em forno resistivo em temperaturas de 1300 ° C por 3h. As amostras foram analisadas através de XRD após o processo de sinterização e as fases foram quantificadas de acordo com o método Rietveld. As imagens foram obtidas por meio de microscopia eletrônica de varredura (MEV) a fim de mostrar as características das microestruturas formadas. De acordo com os resultados, a formação do CT depende da razão molar entre os cátions de cálcio e titânio nas composições.

Characteristics of PEO Incorporated with CaTiO3 Nanoparticles: Structural and Optical Properties

In this research, direct band gap polymer composites with amorphous phase, which are imperative for optoelectronic devices applications were synthesized. The solution cast technique was used to produce polyethylene oxide (PEO)/calcium titanate (CaTiO3) nanocomposite (NC) films. The X-ray diffraction (XRD) confirms the growth of amorphous nature within PEO with CaTiO3 addition. The optical band gaps of pure PEO and PEO/CaTiO3 NC films were calculated using analysis of ultraviolet–visible (UV-Vis) spectra. The change in absorption edge toward lower photon energy is evidence of polymer modification. The dispersion behavior of the refractive index of PEO was manipulated to a higher wavelength upon doping with CaTiO3. Upon adding CaTiO3 to the pure PEO polymer, the dielectric constant and refractive index were considerably modified. The band gap shifts from 4.90 eV to 4.19 eV for the PEO incorporated with an optimum portion of 8 wt. % of CaTiO3. The types of the electronic transition in composite samples were specified, based on the Taucs model and the optical dielectric loss. The alteration of UV/Vis absorption spectra of the NC film was considered a suitable candidate to be applied in nanotechnology-based devices. The spherulites ascribed to the crystalline phase were distinguished through the optical microscopy (OM) study.