Advances in Science and Technology Vol. 118

Abstract: The BaTi_0.88Zr_0.12O₃ ceramic has been synthesized by using a conventional solid-state reaction method and sintered at 1450 °C in air for 3 hours. The structural and dielectric properties of the sample were investigated. It was found that the sample exhibited tetragonal structure with space group P4mm. The maximum dielectric constant, ε_r value was obtained at T_c (70 °C) about 2800 measured at 1 kHz. The dielectric peak was broad which might be due to the pinching effect. However, maximum ε_r value was quite low may be attributed by the T_c and other phase transition point might be not fully coalescence. Another phase transition temperature was vaguely observed around 30 °C to 40 °C. The dielectric properties of the sample were dominated by the grain effect with capacitance values lie within range of 10^-10 to 10^-9. The SEM images shows that the average grain size of the sample was quite small about 2.9087 μm. It might be due to the contribution of Zr⁴⁺ with lower grain growth rate.

Abstract: Barium strontium titanate (BST), Ba_0.8Sr_0.2TiO₃ ceramic prepared using conventional solid-state reaction method has achieved a single phase at 1400 °C. The Ba_0.8Sr_0.2TiO₃ ceramic shows the highest dielectric constant and capacitance at 65°C about 4001 (10 Hz) and 2.92765 x10^-9 F, respectively. The conductivity of Ba_0.8Sr_0.2TiO₃ ceramic is in between the range of semi-insulator and insulator materials, and this composition also has exhibited the positive temperature coefficient resistivity (PTCR) properties jump of one order of magnitude from 2.06202 x 10⁷ Ω.cm to 3.00958 x 10^8­ Ω.cm measured at 1 kHz.

Abstract: Breakdown voltage happens when an electrically insulating material, exposed to a sufficiently high voltage, then instantly becomes an electrical conductor, and flows through it with electrical current. However, a high breakdown voltage would give a low-power efficiency which is bad for Switched Mode Power Supply (SMPS) devices. Also, it would lead to low efficiency. Therefore, a low efficiency leads to a bad system’s performance, and the switching characteristics would also decrease. This in return, cannot be applied to power electronics such as switching devices. Therefore, this work focused on decreasing the breakdown voltage in a DC-DC converter for a step-down chopper circuit or buck converter. The simulation of the circuit is done by using the LTSpice software. The parameters varied are the input voltage, capacitor, and duty cycle. The input voltage supplied to the circuit is 12V and the output voltage obtained is half of the input voltage at the steady-state response. Where this proves the decrement of the breakdown voltage in the chopper circuit.