Oriented, single phase thin films (∼5000 A thick) of Ba0.5Sr0.5TiO3 (BST) have been deposited onto (100) MgO and (100) LaAlO3 (LAO) substrates using pulsed laser deposition. The capacitance and dielectric Q (1/tan δ) of as-deposited and annealed films have been measured from 1 to 20 GHz as a function of electric field (0–80 kV/cm) at room temperature using interdigitated Ag electrodes deposited on top of the film. For films deposited onto MgO, it is observed that, after a postdeposition anneal (1000–1200 °C), the dielectric constant decreases and the dielectric Q increases. For films deposited onto LAO, a postdeposition anneal (⩽ 1000 °C) resulted in a significant increase in the dielectric constant and a decrease in Q. The observed dielectric properties of the BST films are attributed to the changes in film stress, which affects the extent of ionic polarization.

The effect of annealing on the microwave properties of Ba0.5Sr0.5TiO3 thin films

The main interest in the area of practical applications of ferroelectrics, particularly at the microwave frequency, is oriented now to room temperature. In this connection, ferroelectrics like BaxSr1−xTiO3 should be carefully studied. Such materials are characterized by the second order phase transition. In a perfect ferroelectric crystal, the phase transition takes place at temperature TC, which is called the Curie temperature. Real (defected) crystals and ceramic samples are characterized by a presence of built-in electric field and mechanical strains. In the case of the real crystal, the temperature of the phase transition TC′, is displaced to lower temperature and the temperature of the maximum of e(T)Tm is displaced to higher value with respect to TC. Thus, for the real ferroelectric sample (not for an incipient ferroelectric), one has TC′<TC<Tm. Some investigators suppose by default that TC′=TC=Tm. Such a supposition is wrong and can lead to an incorrect treatment of experimental results. In the cas...

Ferroelectric phase transition and maximum dielectric permittivity of displacement type ferroelectrics (BaxSr1−xTiO3)

BaFe12−xGaxO19 (x ≤ 1.2) hexaferrites were synthesized via the usual ceramic technology. It has been established that with an increase in x, the unit cell and magnetic parameters monotonically decrease. The frequency of natural ferromagnetic resonance firstly decreases from 49.6 GHz down to 49.1 GHz when x = 0.6, and then it increases up to 50.5 GHz. The line width monotonically increases from 3.5 GHz up to 5 GHz. The peak amplitude of the resonant curve changes slightly with the exception of when x = 0.9, when it reaches −16 dB. The 1.3 GHz kOe−1 frequency shift in the bias field is more intensive for small values, when x = 0.3. The decreasing values of the magnetic parameters are a result of the dilution of Fe3+–O2−–Fe3+ superexchange interactions. The behavior of the amplitude-frequency characteristics is largely determined through the reduction of uniaxial exchange anisotropy. The prospects of Ga-substituted hexaferrites acting as a material that effectively absorbs the high-frequency electromagnetic radiation are shown.

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Investigation into the structural features and microwave absorption of doped barium hexaferrites

An investigation of the magnetic anisotropy change in BaFe12−2xTixCoxO19 single crystals

Effect of gallium doping on electromagnetic properties of barium hexaferrite

Preparation and properties of (Ba, Sr)TiO3 single crystals

Anisotropy fields and FMR linewidth in single-crystal Al, Ga and Sc substituted hexagonal ferrites with M structure

The cation distribution in Ga, Al and Sc substituted YIG has been determined from 4\piM_{s} measurements at 295K and 77K of annealed and quenched spheres made from single crystals. The effects of thermal treatment on 4\piM_{s} show quantitatively agreement with calculations from the molecular field theory and Borghese's thermodynamic equilibrium expression. The stabilization energies describing quantitatively the lattice site preference of the substituted cations have been determined to: E_{s} = 0.246 \pm 0.01 eV for Ga, E_{s} = 0.15 \pm 0.02 eV for Al and E_{s} = -0.35 \pm 0.03 eV for Sc. The observed kinetics of the cation transfer strongly depend on the temperature, the kind of cation substituted and on the defect concentration. Annealing in inert and reducing atmosphere decreases the relaxation rate of the redistribution by several orders of magnitude. FMR linewidth data indicate the creation of Fe2+which is known to enhance rigorously the cation transfer.

F. Welz

Papers

Preparation and properties of (Ba, Sr)TiO3 single crystals

Anisotropy fields and FMR linewidth in single-crystal Al, Ga and Sc substituted hexagonal ferrites with M structure

Annealing effects on cation distribution in diamagnetically substituted single crystal Yttrium Iron Garnet