Structural, optical, and electrical properties of bulk single crystals of InAsxSb(1-x) grown by rotatory Bridgman method

Radially-homogeneous and single-phase InAsxSb(1−x) crystals, up to 5.0 at. % As concentration, have been grown using the rotatory Bridgman method. Single crystallinity has been confirmed by x-ray and electron diffraction studies. Infrared transmission spectra show a continuous decrease in optical energy gap with the increase of arsenic content in InSb. The measured values of mobility and carrier density at room temperature (for x = .05) are 5.6×104 cm2/V s and 2.04×1016 cm−3, respectively.

Effect of particle size on the giant magnetoresistance of La0.7Ca0.3MnO3

Effect of particle size on the electron transport and magnetic properties of La0.7Ca0.3MnO3 has been investigated. While the ferromagnetic Tc, low field magnetic susceptibility, and insulator‐metal transition are markedly affected by the particle size, the maximum magnetoresistance exhibited by the samples near Tc is not sensitive to the particle size. However, the magnetoresistance at 4.2 K increases with decrease in particle size, suggesting a substantial contribution by the grain boundaries. Preliminary measurements on La0.7Sr0.3MnO3 samples of different particle sizes also corroborate the above conclusions.

Field-induced dielectric properties of laser ablated antiferroelectric (Pb0.99Nb0.02)(Zr0.57Sn0.38Ti0.05)0.98O3 thin films

Niobium-modified lead zirconate stannate titanate antiferroelectric thin films with the chemical composition of (Pb0.99Nb0.02)(Zr0.57Sn0.38Ti0.05)0.98O3 were deposited by pulsed excimer laser ablation technique on Pt-coated Si substrates. Field-induced phase transition from antiferroelectric to ferroelectric properties was studied at different fields as a function of temperature. The field forced ferroelectric phase transition was elucidated by the presence of double-polarization hysteresis and double-butterfly characteristics from polarization versus applied electric field and capacitance and voltage measurements, respectively. The measured forward and reverse switching fields were 25 kV/cm and 77 kV/cm, respectively. The measured dielectric constant and dissipation factor were 540 and 0.001 at 100 kHz, respectively, at room temperature.

Colossal magnetoresistance in epitaxial La(1-x-y)NayMnO3 thin film

We have synthesized La0.83Na0.11MnO2.93 by heating La2O3 and MnCO3 in NaCl melt at 900 °C. The exact composition was arrived by analyzing each ion by an independent chemical method. The compound crystallized in a rhombohedral structure and showed an insulator-to-metal transition at 290 K. Epitaxial thin films were fabricated on LaAlO3 (100) using a pulsed laser deposition technique. The film also showed an insulator-to-metal transition at 290 K. Magnetoresistance [ΔR/R0 = (RH−R0)/R0] was −71% near the insulator-to-metal transition temperature of 290 K at 6 T magnetic field.

Electron paramagnetic resonance study of porous silicon

Electron paramagnetic resonance studies under ambient conditions of boron‐doped porous silicon show anisotropic Zeeman (g) and hyperfine (A) tensors, signaling localization of the charge carriers due to quantum confinement.

Alloying induced degradation of the absorption edge of InAsxSb1-x

InAsxSb1−x alloys show a strong bowing in the energy gap, the energy gap of the alloy can be less than the gap of the two parent compounds. The authors demonstrate that a consequence of this alloying is a systematic degradation in the sharpness of the absorption edge. The alloy disorder induced band-tail (Urbach tail) characteristics are quantitatively studied for InAs0.05Sb0.95.

Analysis of a cascade‐pumped 16 μm CO2‐N2 downstream‐mixing gasdynamic laser

The generation of a 16 μm laser beam through cascading in a downstream‐mixing CO2 gasdynamic laser is studied. To simulate actual lasing action, a generalized, two‐dimensional, flow‐radiation‐coupled power extraction model for a gasdynamic laser is used. Also, to model the cascade process a new four‐mode CO2‐N2 vibrational kinetic model has been proposed. The steady‐state intensity obtained for an exclusive 9.4 μm transition is of the order of 5×107 W/m2. In the cascade mode of operation the steady‐state intensities for 9.4 and 16 μm transitions of the order of 5×107 W/m2 and 1.0×106 W/m2, respectively, have been obtained.

Colossal electroresistance and current induced switching in ferromagnetic insulating state of La0.82Ca0.18MnO3

Colossal electroresistance and current induced resistivity switching have been measured in the ferromagnetic insulating (FMI) state of single crystal manganite La0.82Ca0.18MnO3. The sample has a Curie transition temperature TC = 165 K and the FMI state is realized for temperatures T<100 K. The electroresistance (ER), arising from a strong nonlinear resistivity, attains a large value ( ≈ 100%) in the FMI state. However, this is accompanied by a collapse of the magnetoresistance (MR) to a small value even in magnetic field (H) of 10 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled.

Dielectric properties of c-axis oriented Zn1-xMgxO thin films grown by multimagnetron sputtering

Zn1−xMgxO (x = 0.3) thin films have been fabricated on Pt/TiO2/SiO2/Si substrates using multimagnetron sputtering technique. The films with wurtzite structure showed a (002) preferred orientation. Ferroelectricity in Zn1−xMgxO films was established from the temperature dependent dielectric constant and the polarization hysteresis loop. The temperature dependent study of dielectric constant at different frequencies exhibited a dielectric anomaly at 110 °C. The resistivity versus temperature characteristics showed an anomalous increase in the vicinity of the dielectric transition temperature. The Zn1−xMgxO thin films exhibit well-defined polarization hysteresis loop, with a remanent polarization of 0.2 μC/cm2 and coercive field of 8 kV/cm at room temperature.

Dual wavelength CO2‐N2‐CS2 gasdynamic laser

A new method for producing simultaneous lasing at 10.6 μm and 38.3 μm in a CO2‐N2‐CS2 gasdynamic laser is presented. The theoretical analysis predicts small‐signal gain values of the order 0.21 m−1 for 10.6 μm lasing in CO2 molecules and 0.085 m−1 for 38.3 μm lasing in CS2 molecules, indicating the possibility of dual wave lasing.

Weakening of charge order and antiferromagnetic to ferromagnetic switch over in Pr0.5Ca0.5MnO3 nanowires

We have prepared crystalline nanowires (diameter ∼ 50 nm, length ∼ a few microns) of the charge-ordering manganite Pr0.5Ca0.5MnO3 using a low reaction temperature hydrothermal method and characterized them using x-ray diffraction, transmission electron microscopy, superconducting quantum interference device (SQUID) magnetometry and electron magnetic resonance measurements. While the bulk sample shows a charge ordering transition at 245 K and an antiferromagnetic transition at 175 K, SQUID magnetometry and electron magnetic resonance experiments reveal that in the nanowires phase, a ferromagnetic transition occurs at ∼ 105 K. Further, the antiferromagnetic transition disappears and the charge ordering transition is suppressed. This result is particularly significant since the charge order in Pr0.5Ca0.5MnO3 is known to be very robust, magnetic fields as high as 27 T being needed to melt it.

Optical diffraction of second-harmonic signals in the LiBO2-Nb2O5 glasses induced by self-organized LiNbO3 crystallites

The nanocrystallites ( ≈ 3 nm) of LiNbO3, evolved in the (100−x)LiBO2-xNb2O5 (5x20, in molar ratio) glass system exhibited intense second-harmonic signals in transmission mode when exposed to infrared (IR) light at λ = 1064 nm. The second-harmonic waves were found to undergo optical diffraction which was attributed to the presence of self-organized submicrometer-sized LiNbO3 crystallites that were grown within the glass matrix along the parallel damage fringes created by the IR laser radiation. Micro-Raman studies carried out on the laser-irradiated samples confirmed the self-organized crystallites to be LiNbO3.

Enhancement of charge and energy storage in sol-gel derived pure and La-modified PbZrO3 thin films

Antiferroelectric lanthanum-modified PbZrO3 thin films with La contents between 0 and 6 at. % have been deposited on Pt(111)/Ti/SiO2/Si substrate by sol-gel route. On the extent of La-modification, maximum polarization (Pmax) and recoverable energy density (W) have been enhanced followed by their subsequent reduction. A maximum Pmax ( ∼ 0.54 C/m2 at ∼ 60 MV/m) as well as a maximum W ( ∼ 14.9 J/cc at ∼ 60 MV/m) have been achieved on 5% La modification. Both Pmax and W have been found to be strongly dependent on La-induced crystallographic orientations.

Antiferroelectriclike polarization behavior in compositionally varying (1-x) Pb(Mg1/3Nb2/3)O3–(x) PbTiO3 multilayers

Compositionally varying multilayers of (1−x) Pb(Mg1/3N2/3)O3–(x) PbTiO3 were fabricated using pulsed laser ablation technique. An antiferroelectriclike polarization hysteresis was observed in these relaxor based multilayer systems. The competition among the intrinsic ferroelectric coupling in the relaxor ferroelectrics and the antiferroelectric coupling among the dipoles at the interface gives rise to an antiferroelectriclike polarization behavior. An increment in the coercive field and the applied field corresponding to the polarization flipping at low temperatures, provide further insight on the competition among the long-range ferroelectric interaction and the interfacial interaction in the polarization behavior of these relaxor multilayers.

Growth and ferroelectric properties of Bi2VO5.5 thin films with metallic LaNiO3 electrodes

Novel ferroelectric bismuth vanadate, Bi2VO5.5 (BVO), thin films have been grown between lattice matched metallic LaNiO3 (LNO) layers deposited on SrTiO3 (STO) by the pulsed laser deposition technique. LNO/BVO/LNO/STO and Au/BVO/LNO/STO trilayer structures exhibited c‐oriented (001) growth of BVO. LNO has been found to be a good metallic electrode with sheet resistance ∼20 Ω in addition to aiding c‐axis oriented BVO growth. The dielectric constant, ϵr of LNO/BVO/LNO/STO, at 300 K was about 12. However, when an Au electrode was used on top of BVO/LNO/STO film, it showed a significant improvement in the dielectric constant (ϵr=123). The ferroelectric properties of BVO thin films have been confirmed by hysteresis behavior with a remnant polarization, Pr=4.6×10−8 C/cm2 and coercive field, Ec=23 kV/cm at 300 K.