Microwave absorption properties of dielectric La1.5Sr0.5NiO4 ultrafine particles

• Colossal permittivity La1.5Sr0.5NiO4 ultrafine particles are prepared.
• The particles have weak paramagnetic behavior at 300 K.
• La1.5Sr0.5NiO4 particles/wax composites exhibit strong microwave absorption.
• Impedance matching is responsible for the absorption resonances.

La2−xSrxNiO4 compounds are well known dielectric materials that have colossal permittivities (ɛR > 107). In the present work, the powder of La1.5Sr0.5NiO4 ultrafine particles was prepared by a combinatorial method of solid-state reaction and high-energy ball milling. Magnetic measurements, M(H), show a very small magnetization and paramagnetic characteristics at room temperature. Flat layers of La2−xSrxNiO4/paraffin mixture of different thicknesses (t) exhibits strong microwave absorption resonances in the 4–18 GHz range. The reflection loss (RL) decreases with t and reaches down to −36.7 dB for t = 3.0 mm. The impedance matching (|Z| = Z0 = 377 Ω), rather than the phase matching mechanism, is found responsible for the resonance for 1.5 mm ≤ t ≤ 3.0 mm. Further increase in the thickness leads to |Z| > Z0 at all frequencies and a reduced absorption. The influence of non-metal backing is also discussed. The obtained low RL suggests that La1.5Sr0.5NiO4 particles could be a potential filler for high performance radar absorbing material.