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Intrinsic and extrinsic dielectric responses of CaCu3Ti4O12 thin films
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Image of FIG. 1.
FIG. 1.

(Color online) Polarized micro-Raman spectra for the CaCu3Ti4O12 film (320 nm) onto a LaAlO3 substrate, for four special scattering configurations that allows for separating the symmetries of the first-order modes of CCTO. Defect modes are indicated by asterisks. The Raman modes of LAO are also indicated.

Image of FIG. 2.
FIG. 2.

(Color online) Top panel: room temperature experimental infrared spectrum (dots) of CCTO film (320 nm) onto the LAO substrate along with its adjustment with the Lorentz oscillator model (black line), which takes into account the LAO substrate contribution (gray line). The CCTO deconvoluted spectrum is shown by the red line. Bottom panels: the temperature behavior of adjusted real parts of the dielectric constant (left) and optical conductivity (right), in the region of the four lowest frequency polar phonons.

Image of FIG. 3.
FIG. 3.

(Color online) Temperature dependence of the “static” infrared dielectric permittivity (ɛr ) for the CCTO films on the LAO substrate for films with 160 nm (red squares) and 320 nm (blue circles). The dashed and solid lines correspond to the fittings to the Curie-Weiss and to Barrett’s equations, respectively.

Image of FIG. 4.
FIG. 4.

(Color online) Top: frequency dependence of the real dielectric permittivity for CCTO films with 160 nm and 320 nm thicknesses, for temperatures ranging from 175 to 375 K. Bottom: thermal evolutions of the real dielectric “constant” for a bulk sample (full symbols, from Ref. 3), and CCTO thin films (semi-hollow symbols for the 320 nm film; hollow symbols for the 160 nm film), for some parameterized frequencies (squares for 20 Hz, circles for 2 kHz, and down triangles for 200 kHz).

Image of FIG. 5.
FIG. 5.

(Color online) The reciprocal temperature dependence of the real part of the ac-electrical conductivity measured for the 320 nm-thick CCTO sample for frequencies ranging from 100 Hz to 1 MHz. The upper inset shows the optical conductivity behavior measured for this material close to the lowest frequency polar phonon; the lower inset shows the optical edge of this film in the visible region.

Image of FIG. 6.
FIG. 6.

(Color online) Top panel: complex impedance plots (Z″ vs Z′) for the 320 nm-thick CCTO film, for several temperatures. Bottom panel: Arrhenius dependencies of the relaxation times determined from the two arcs of the top panel. The red circles are data for the main higher frequency relaxation and the blue triangles are for the lower frequency one.


Generic image for table
Table I.

Infrared dispersion parameters: TO phonon wavenumbers (Ω j , TO ) and dampings (γj , TO ) in cm−1, and dielectric strengths (Δɛj ), obtained from the fittings of the 320 nm CCTO thin film on LAO substrates, at 5 K and 300 K. Two extra modes, likely activated by defects (around 175 cm−1) or LAO leakage (187 cm−1), are in parentheses.

Generic image for table
Table II.

Infrared TO phonon wavenumbers (in cm-1) obtained for the 320 nm and 160 nm CCTO thin films onto LAO substrates, at low and room temperatures, compared with reported data for single crystals (Refs. 14 and 36) and thin films (Ref. 25).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Intrinsic and extrinsic dielectric responses of CaCu3Ti4O12 thin films