Giant dielectric response in two-dimensional charge-ordered nickelate ceramics
ABSTRACT Dielectric relaxations of charge-ordered Ln 1.5 Sr 0.5 NiO 4 ( Ln = La and Nd) ceramics were investigated over a broad temperature range. The giant dielectric constant (over 70 000 ) with a low dielectric loss of ∼0.1 was determined at high frequencies (up to 5 MHz) over a broad temperature range. There are two dielectric relaxations in the vicinity of charge ordering temperatures. The thermal activated small polaronic hopping between two charge ordering temperatures should contribute to the giant dielectric response in the present ceramics. Compared to other giant dielectric constant materials, the present materials have the notable advantage for high frequency applications.
SourceAvailable from: Shujun ZhangScientific Reports 02/2015; 5:8295. · 5.08 Impact Factor
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ABSTRACT: The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I-V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I-V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I-V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I-V behavior of (Nb + In) co-doped TiO2 ceramics.Scientific Reports 02/2015; 5:8295. DOI:10.1038/srep08295 · 5.08 Impact Factor
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ABSTRACT: The pristine layered cuprate Pr2CuO4 samples of >95% density were fabricated as thin disks. The samples, analyzed by X‐ray diffraction and Scanning electron microscopy, showed clean T′‐type phase with Rietveld refined lattice parameters a = b = 3.95805(±5) Å and c = 12.2262(±5) Å. The measured dielectric properties of the Pr2CuO4 ceramics, in the temperature range −100°C–150°C and frequencies (ν) 0.1 Hz–1 MHz, showed extremely high εr′ > 104 (above −30°C), and dissipation (tan δ = εr′′/εr′) between 0.1 and 5 (for 500 Hz ≤ ν ≤ 1 MHz, and −100 ≤ T ≤ 150°C). The ac conductivity of Pr2CuO4 ceramics ranged between 10−6 and 10−3 Scm−1 for the measured frequencies and temperatures, and showed frequency‐dependent double power law behavior akin to a modified Jonscher's power law.Journal of the American Ceramic Society 07/2013; 96(7). DOI:10.1111/jace.12306 · 2.43 Impact Factor