Elastic, dielectric and piezoelectric anomalies and Raman spectroscopy of 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3

The solid solution 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) is a promising lead-free piezoelectric material with exceptionally high piezoelectric coefficients. The strong response is related to structural instabilities close to ambient temperature. We report here on temperature-induced anomalies in the dielectric, piezoelectric, and elastic coefficients and Raman spectroscopy of ceramic BCZT. The data indicate ferroelectric-ferroelectric structural phase transitions in this material in addition to those previously reported. An anomaly is also observed above the Curie temperature TC and is associated with the loss of polar structure that persists thirty degrees above TC

The Structural Complexity of (Bi0.5Na0.5)TiO3-BaTiO3 as Revealed by Raman Spectroscopy

The structural phase diagram of the Pb-free ferroelectric (Na1/2Bi1/2)1-xBaxTiO3 (NBT-BT), x<0.1, has been explored by Raman spectroscopy at temperatures from 10 to 470 K. The data provide clear evidence for a proposed temperature-independent morphotropic phase boundary at x \approx 0.055. However, there is no evidence for a structural phase transition across T \approx 370 K for x > 0.055, where bulk-property anomalies appear to signal a transition to a nonpolar or antiferroelectric phase. The results identify that the phase above 370 K shows short-range ionic displacements that are identical to those in the long-range-ordered phase below 370 K. These conclusions provide a natural interpretation of the weak piezoelectric response in this system and have important implications for the search for Pb-free piezoelectrics.Comment: 21 pages, 5 figure

Effect of K0.5Na0.5NbO3 on Properties at and off the Morphotropic Phase Boundary in Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 Ceramics

Lead-free (1 - y)(Bi1/2Na1/2TiO3-xBi(1/2)K(1/2)TiO(3))-yK(0.5)Na(0.5)NbO(3) [(1 - y)(BNT-xBKT)-yKNN] (0.1 &lt;= x &lt;= 0.6 and 0 &lt;= y &lt;= 0.05) ceramics were prepared with compositions both at as well as off the morphotropic phase boundary (MPB) of x = 0.2 and y = 0. It was found that KNN addition destabilizes a ferroelectric order in BNT-BKT at zero electric-field, resulting in low remanent polarization, remanent strain and effective small signal d(33,eff) [23 pC/N for (x, y) = (0.2; 0.05), 60 pC/N for (0.2; 0.02)], while it does not affect the maximum polarisation and strain at high fields and thus enhances large signal piezoelectric coefficient, d*(33) [200 pm/V for (0.2; 0.05), 217 pm/V for (0.2; 0.02)]. This effect of KNN was found to be independent from the MPB and thus equally high d*(33) values were obtained for compositions at and far off the MPB. Thus, adding KNN to BNT-BKT removes the restriction to remain at exactly MPB position and provides more flexibility while offering equal or even improved strain.close141

Ohmic contacts of Au and Ag metals to n-type GdN thin films

The rare-earth nitrides appear as attractive alternatives to dilute ferromagnetic semiconductors for spintronics device applications. Most of them combine the properties of the ferromagnet and the semiconductor, an exceedingly rare combination. In this work we have grown n-type polycrystalline semiconducting GdN layers between pre-deposited contacts made of Cr/Au and Cr/Ag. The resistivity of the GdN layers ranges from 4.4×10-4 Ωcm to 3.1×10-2 Ωcm depending on the nitrogen pressure during the growth. The electrical properties of metal/n-type GdN/metal planar junctions are investigated as a function of the temperature. The current voltage characteristics of the junctions were linear for temperatures ranging from 300 K down to 5 K, suggesting an ohmic contact between the Au or Ag metal and the n-type GdN layer

Sea ice growth rates from tide-driven visible banding

In this paper, periodic tide-current-driven banding in a sea-ice core is demonstrated as a measure of the growth rate of first-year sea ice at congelation-ice depths. The study was performed on a core from the eastern McMurdo Sound, exploiting the well-characterized tidal pattern at the site. It points the way to a technique for determining early-season ice growth rates from late-season cores, in areas where under ice currents are known to be tidally dominated and the ice is landfast, thus providing data for a time of year when thin ice prevents direct thickness (and therefore growth rate) measurements. The measured results were compared to the growth-versus-depth predicted by a thermodynamic model.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Facile dissociation of molecular nitrogen using lanthanide surfaces: towards ambient temperature ammonia synthesis

A combined experimental and computational study is reported on a hitherto unrecognised single lanthanide catalyst for the breaking of molecular nitrogen and formation of ammonia at ambient temperature and low pressure.We combine in situ electrical conductance and electron diffraction measurements to track the conversion from the lanthanide metals to the insulating lanthanide nitrides.The efficiency of the conversion is then interpreted using DFT+U calculations, suggesting a molecular nitrogen dissociation pathway separate from that well-established for transition metals.Finally, we show that exposure of the lanthanide surfaces to both molecular nitrogen and hydrogen results in the formation of ammonia.<br /