Electrical characterization of nickel manganite powders in high-frequency range

This paper presents a study of electrical properties of nickel manganite powder (NiMn2O4, NTC thermistor material) in a wide frequency range up to 1 GHz, which is much needed for the development of NTC thermistors for mobile phones and other RF and microwave devices. The permittivity of nickel manganite has been analyzed as a function of frequency (100 MHz–1 GHz) and temperature (30–100 °C), as well as for mechanically activated powders (milled for 5, 30 and 45 min). To accurately measure the permittivity we have developed a robust, fast and low-cost device that enables repeated measurements at various temperatures. The detailed description of the device is given, and the method to determine permittivity of the sample is explained. We have found that the permittivity of nickel manganite powder decreases with the frequency for over 15%. In the same time, permittivity increases for almost 40% with the milling time and around 5% with the temperature.

► Characterization of NTC powders in a wide frequency and temperature range is made.
► Relative permittivity of NTC materials in the form of as-prepared powder determined.
► Measurement device for characterization of materials in powder form is proposed.