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Lead-free multiferroic bilayer thin films were fabricated on (111)Pt/Si substrate via a simple sol-gel chemical solution deposition, by altering the position of piezoelectric (Ba0.85Ca0.15) (Ti0.9Zr0.1)O3 (BCTZO) and ferromagnetic CoFe2O4 (CFO). Single layer BCTZO experiences the out-of-plane compressive stress, while this layer is under tensile strain in both the bilayers. The microstructural study confirms the formation of bilayers with expected chemical composition composed of multiple well-developed crystallites having no crystallographic dependencies. Thin films of BCTZO and CFO/BCTZO exhibited saturated ferroelectric hysteresis loops at room temperature with a Pr of 7.2 and 5.6 μC/cm2. The magnetic field induced shift in phonon vibrations coupled with direct magnetoelectric (ME) measurements demonstrated a stress-mediated coupling mechanism in the bilayers. We found a superior ME coefficient (105 MV/cm Oe) and dielectric tunability (∼52%) for CFO/BCTZO bilayer compared to the BCTZO/CFO bilayer, which demonstrates that the modification of strain state in bilayers is useful for the desired ME coupling. The BCTZO having piezoelectricity on par with that of lead-based ones can be useful to tailor lead-free ME applications.

In this work, phosphate-borate based glasses with molar composition 20.7P2O5–17.2Nb2O5–13.8WO3–34.5A2O–13.8B2O3, where A = Li, Na, and K, were prepared by the melt quenching technique. The as-prepared glasses were heat-treated in air at 800 °C for 4 h, which led to the formation of glass-ceramics. These high chemical and thermal stability glasses are good candidates for several applications such as fast ionic conductors, semiconductors, photonic materials, electrolytes, hermetic seals, rare-earth ion host solid lasers, and biomedical materials. The present work endorses the analysis of the electrical conductivity of the as-grown samples, and also the electrical, dielectric, and structural changes established by the heat-treatment process. The structure of the samples was analyzed using X-Ray powder Diffraction (XRD), Raman spectroscopy, and density measurements. Both XRD and Raman analysis confirmed crystals formation through the heat-treatment process. The electrical ac and dc conductivities, σac and σdc...

Rare-earth orthoniobates constitute a class of materials that has been exploited due to their interesting physical properties depending on the lanthanide element. Besides paramagnetism, ferroelasticity, and negative compressibility, these materials are known by their interesting optical properties and mixed types of conduction processes (protonic, ionic, and electronic). In this work, two types of SmNbO4 samples were studied: polycrystalline samples, prepared by a sol-gel route using the Pechini method, and single crystalline fibres grown by the Laser Floating Zone technique. These samples were structurally characterized based on powder and single-crystal X-ray diffraction studies. A metastable tetragonal phase, stabilized by grain size, was identified in the synthesized powders. After a sintering process of such powders, a single monoclinic phase was obtained. Complementarily, scanning electron microscopy and Raman spectroscopy analyses were performed to these samples. Photoluminescence and photoluminescence excitation spectroscopic studies allowed identifying more than one optically active centre of the trivalent samarium ion in the analysed material. Impedance spectroscopy measurements have shown a large variation of the ac conductivity as a function of temperature, assigned to a protonic conduction and to native ionic conduction mechanisms.

Polycrystalline samples of a layered magnetic ceramic oxide, Ba2Co2Fe12O22 (Co2Y), doped with Bi2O3 were prepared by the solid state reaction method. The dielectric impedance properties were studied over the range of frequency between 1 Hz–1MHz and in the temperature range of 313–493 K, using the modulus formalism. The impedance plot showed a first semicircle at high frequency which was assigned to the grain intrinsic effect and a second semicircle, at lower frequencies, which corresponds to grain boundary polarization (conduction phenomenon). A complex modulus spectrum was used to understand the mechanism of the electrical transport process, which indicates that a non-exponential type of conductivity relaxation characterizes this material. The values of the activation energy of the compound (calculated both from dc conductivity and the modulus spectrum) are very similar, suggesting that the relaxation process may be attributed to the same type of charge carriers. The dielectric measurements were studied ...

A thorough investigation of the ac electrical properties of carbon black (CB) mixed into ethylene butylacrylate copolymer has been conducted using ac impedance spectroscopy in the frequency range 10 Hz–100 kHz and over the temperature range of 150 (Tg−48 K)–319 (Tg+121 K) K. For this investigation, a series of eight samples were prepared with various filler contents above the percolation threshold. Using the electric modulus formalism it has been found that the Cole–Cole equation of dielectric relaxation expressed in the electric modulus form is capable of quantitatively describing the experimental data from which we extract the relaxation time and a parameter α which gauges the broadening of the loss spectrum. The small values of α ranging from 0.06 to 0.10 suggest a behavior close to the state of a single relaxation time. Furthermore, the relaxation time as a function of temperature is characterized by an Arrhenius behavior. While the effective activation energy is on the order of 60 meV and is insensitive to CB volume fraction, the Arrhenius prefactor is found to strongly depend on this volume fraction. The observed relaxation mechanism does not result simply from thermally activated dipolar interactions but is a collective cooperative effect of the CB mesostructure.