In Honor of Nobel Laureate Dr. Avram Hershko
In the electrodynamic properties study of new AlN- 5wt.%C(diamond powder)-5wt.%Mo composite materials the values and behavior of the real and imaginary parts of the microwave permittivity were determined and the optimal technological process for materials synthesis was established. The materials with density 3.16 g/cm3 and 3.30 g/cm3 were obtained by the pressureless sintering (PS) at the temperature of 1850 °C and by the hot pressing (HP) at the temperature of 1820 °C (pressure of 15 MPa), respectively.
The microstructure and phase composition of the composite materials were studied using a scanning electron microscope and the X-ray diffractometer Ultima IV (Rigaku, Japan) with the Rietveld method for data analysis. The imaginary and real parts of the permittivity were measured by the microwave vector network analyzer Keysight PNA N5227A in the frequency range of 26 - 40 GHz.
The results of structural studies showed that sintering of composites by different methods results in almost unchanged their phase composition, and the main phases are AlN, Al3(O,N)4, Mo2C, Y3Al5O12, and C (graphite) - as in [1].
It was determined that the real part of the permittivity (ε') for both composites obtained by the PS and HP methods is practically frequency independent between 26 to 36 GHz with the value of about 8 and 27 , respectively. At the same time, the imaginary part of the permittivity (ε″) increases from 0.29 to 1 and from 3.46 to 5.56 for materials made by the PS and HP methods, respectively. When the test frequency is increased from 36 to 40 GHz, significant fluctuations in the permittivity values are observed, which is possibly related to the greater intensity of electromagnetic wave internal reflections due to the peculiarities of the formation of the materials structure.
As a result of the research, it was established that composite materials obtained by the hot pressing method are characterized by higher density and higher values of the real part of the permittivity in the frequency range 26 - 36 GHz.
