The frequency dependence of the complex permittivity (ε∗=ε′-jε″) of Ba0.5Sr0.5TiO3 0.3-μm-thick film is measured up to 110 GHz by using interdigitated capacitors and coplanar waveguides. It is shown that the temperature dependence (from 77 to 373 K) of microwave losses, measured at 20 GHz, is described by a tan(δ)-(ε′)3/2 law. This result indicates distributed electromagnetic wave interactions with the local soft-phonon modes. This conclusion is further confirmed by the satisfactorily fit of the frequency dependence of the complex permittivity by a Cole–Cole function with an exponent β=0.6 and a characteristic time τ=0.21 ps.
Ceramics of the La 2 O 3 -TiO 2 system have very good dielectric properties, which make La 2 Ti 2 O 7 a good candidate for microwave applications. Using radio-frequency magnetron sputtering, we have deposited LaTiO x N y oxynitride thin films on (0 0 1) strontium titanate and glass substrates, starting from a homemade oxide target. The microwave dielectric properties of La 2 Ti 2 O 7 ceramic have been investigated in the 100 Hz to 10 GHz range in order to have a reference for further studies. The evolution of ε and ε shows a space charge domain with a critical frequency F c = 1 GHz. Measurements in the temperature range from 20 to 880 • C have been carried out to study phase transitions and conduction mechanisms.
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