Particle distribution of the reagent powders in the fabrication process

Particle distribution of the reagent powders in the fabrication process can be controlled to obtain homogeneous ceramics with a small dielectric loss, which is very crucial for many applications. Ultrasonication or conventional milling methods can be used in the homogenization process. The processes not only homogenize the powders but also decrease the particle size of the powders and activate them [31,16,27,17,24,1,2]. Mechanical milling of the powder is one of the common methods for the homogenization process. In the conventional mechanical milling process, the powders in the shaker are subjected to high-energy collisions from the balls. But it order ryanodine is difficult to obtain a homogeneous mixture with the uniform particles of the powder; that effect appeared clearly after sintering as different grain walls [12]. The particle size of the powder can be controlled by the ultrasonic method, which is based on the acoustic cavitation phenomenon. High-intensity ultrasonic waves generate, enlarge and collapse a lot of bubbles in the liquid [6,7]. Collapsing bubbles produce micro/nano dots with local high temperatures and intense pressure. High temperatures and intense pressure deagglomerate the grains of the powder. Recently, micro/nano-materials have been successfully prepared by the ultrasonic method, including BaCO3[3], CuInS2[25], SiC [21], Mg(OH)2 and MgO [4].
In this study, new ultrasonication and conventional mechanical milling methods used for the homogenization of reagent powders to obtain pure and Nb-doped BaTiO3 ceramics in the solid-state reaction process. We have compared two methods to discover to homogenization and deagglomeration effects on structural and dielectric properties of pure and Nb-doped BaTiO3 ceramics.

Experimental procedure
BaCO3, TiO2, and Nb2O5were purchased from Alfa Aesar (UK) and were used as analytical grades (>99.5%). BaTiO3-based ceramics with Nb additives (%0.0, and% 1.0 w) were prepared using the solid-state reaction method. The powders were homogenized by two methods:
After homogenization, the powder mixtures were dried in a drying oven at 120°C for 1h. The obtained powders were calcined at 1100°C for 4h in alumina crucibles. Table 1 shows the experimental conditions. The structures of the powders were confirmed by Fourier transform infrared spectroscopy (FTIR) (Shimadzu, IRAffinity-1S, Japan) and X-ray diffraction (XRD) with (Rigaku, Smart Lab, Japan) diffractometer. FTIR analysis was performed in the range of 400–4000cm−1 with a signal-to-noise (S/N) ratio of 30,000:1 (the peak-to-peak resolution is 0.5cm−1 at the neighborhood of 2100cm−1). XRD analysis was obtained in the range of 10°⩽2θ⩽90° with CuKα radiation. The surface morphologies of the powders were analyzed using Scanning Electron Microscopy (SEM) (JEOL, 5500, Japan). The calcined powders were pressed into pellets that were approximately 10mm in diameter and 2mm thick by a computer-controlled press. The pellets were sintered at 1300°C for 2h to achieve dense ceramic pellets. SEM images were used to analyze the morphologies of the sintered pellets. Complex impedance measurements of the samples were carried out using an Agilent E4980A LCR meter at oscillation amplitude of 1V. Complex permittivity (, ) and complex AC conductivity (σ′ and σ″) were analyzed in a wide frequency range of 20Hz to 2MHz at room temperature.

Results

Discussion
An ultrasonic processor with high-intensity ultrasonic waves based on the acoustic cavitation phenomenon or the conventional mechanical milling method with zirconia balls could be used to homogenize and deagglomerate the powders in the first step of the solid-state processes. These processes have also activated the powders and improved the structure and dielectric properties of the ceramics [16,31,27,17,24]. The homogenization process’ effects on the structures and dielectric properties of undoped and Nb-doped BaTiO3 ceramics prepared using the ultrasonic method and the conventional mechanical milling method have been investigated.