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The use of lead-free materials has recently become a very important issue in environmental protection of the earth. Two groups of lead-free ceramics, (K0.5,Na0.5)NbO3 based (KNN) and Bi1-y(NaxK1-x)yTiO3 based (BNKT), were studied for their thermal, dielectric, and pyroelectric properties as candidates for pyroelectric sensor applications. The BNKT-based ceramic, [Bi0.5(Na0.94K0.05Li0.016)0.5]0.95Ba0.05TiO3 (BNKLBT), shows excellent pyroelectric properties when compared with KNN-based ceramic and lead zirconate titanate. Its properties were measured as follows: pyroelectric coefficient p=360 μC/m2 K, pyroelectric figure of merit of current, voltage, and detectivity Fi=221 pm/V, Fv=0.030 m2/C, and Fd=14.8 μPa-1/2. With these outstanding pyroelectric properties, the BNKLBT ceramic can be a promising material for pyroelectric sensor applications. The BNKLBT ceramic with different thicknesses (i.e., 0.3, 0.5, and 0.7 mm) have been used as the sensing element for fabricating infrared detectors. The current responsivity of the sensors was evaluated as functions of frequency. [ABSTRACT FROM AUTHOR]

Carbon and titanium concurrently doped MgB2 alloys with a composition of Mg1-xTixB2-yCy have been prepared by an in situ solid state reaction method. The combination effects of carbon and Ti doping on structure, microstructure, irreversibility field (Hirr), and critical current density (Jc) of MgB2 have been investigated. It is found that doping Ti in MgB2 does not reduce the solubility of carbon in MgB2, but, on the contrary, it eliminates the porosity present in the carbon-doped MgB2, resulting in an improved intergrain connectivity. As a result, Jc and Hirr of MgB2 have been significantly improved, sharply contrasted to the situation of C-only-doped or Ti-only-doped MgB2 bulks. Our results clearly reveal that carbon and Ti codoping are largely cooperative in improving the performance of MgB2 in the high magnetic fields (>3 T) and at high temperature (∼20 K). [ABSTRACT FROM AUTHOR]

Ti-doped MgB[sub 2]/Cu tapes with Ta as a buffer layer were prepared through the in situ powder in tube method by using Mg, Ti, and B powders. The phase compositions, microstructure features, and superconducting properties were investigated by x-ray diffraction, scanning electron microscope, and superconducting quantum interference device magnetometer. It is found that TiB[sub 2] phase was formed in Ti-doped MgB[sub 2] tape. Magnetization measurement results show that the critical transition temperature of MgB[sub 2]/Ta/Cu tape with Ti doping is around 38 K. The irreversibility field H[sub irr] and critical current density J[sub c] can be greatly enhanced by Ti doping. H[sub irr] of the Mg[sub 0.9]Ti[sub 0.1]B[sub 2] tape is as high as 7.4 T at 10 K. The high critical current density J[sub c] of 1.5 × 10[sup 6] A/cm² (10 K, self field) and 9.3 × 10[sup 5] A/cm² (20 K, self field) are obtained in the Mg[sub 0.9]Ti[sub 0.1]B[sub 2] tape. In addition, a suitable amount of Ti doping can lead to a high density and fine grain size of MgB[sub 2], which may be the reason for high J[sub c] in Ti-doped MgB[sub 2] tapes. [ABSTRACT FROM AUTHOR]

We prepared a series of Mg[sub 1-χ]Zr[sub χ]B[sub 2] bulk samples with different x values by the solid-state reaction at ambient pressure and investigated the effects of the Zr doping on phase compositions, microstructure, and flux pinning behavior. The results indicate that the a axis increases with the increase of the Zr doping and the c axis remains unchanged. ZrB[sub 2] phases form and a small amount of Zr atoms may substitute Mg in Zr-doped samples. Critical temperature drops with increasing the Zr doping. It is found that critical current density J[sub c] can be significantly enhanced by the Zr doping and the best data are achieved in Mg[sub 0.9]Zr[sub 0.1]B[sub 2]. For this sample, J[sub c] values are remarkably improved to 1.83 × 10[sup 6] A/cm² in the self field and 5.51 × 10[sup 5] A/cm² in 1 T at 20 K. Also, the irreversibility field is increased by the Zr doping. The high density, fine grain size of MgB[sub 2], and small ZrB[sub 2] particles in Zr-doped samples may be responsible for the enhancement of J[sub c]. Also, the field dependence of J[sub c] at different temperatures was briefly discussed. [ABSTRACT FROM AUTHOR]

Grain boundaries (GBs) of YBa[sub 2]Cu[sub 3]O[sub y] (YBCO) are preferentially doped with Ag by the solid-state diffusion method. The distribution of Ag is highly localized in the GB. As a result of the Ag doping, the J[sub c]-H behavior of YBCO textured polycrystalline samples is significantly improved, and at 60 K and 7 T, J[sub c] is tripled. It is proposed that Ag could partially replace the Cu in CuO[sub 2] planes near GBs, therefore reducing the geometric distortion of Cu-O bonds and making the effective GBs thinner. [ABSTRACT FROM AUTHOR]

Carbon and titanium concurrently doped MgB2 alloys with a composition of Mg1-xTixB2-yCy have been prepared by an in situ solid state reaction method. The combination effects of carbon and Ti doping on structure, microstructure, irreversibility field (Hirr), and critical current density (Jc) of MgB2 have been investigated. It is found that doping Ti in MgB2 does not reduce the solubility of carbon in MgB2, but, on the contrary, it eliminates the porosity present in the carbon-doped MgB2, resulting in an improved intergrain connectivity. As a result, Jc and Hirr of MgB2 have been significantly improved, sharply contrasted to the situation of C-only-doped or Ti-only-doped MgB2 bulks. Our results clearly reveal that carbon and Ti codoping are largely cooperative in improving the performance of MgB2 in the high magnetic fields (>3 T) and at high temperature (∼20 K). [ABSTRACT FROM AUTHOR]