High-resolution synchrotron XRD study of Zr-rich compositions of Pb(Zr_xTi_1-x)O_3 (0.525\leq x \leq 0.60): evidence for the absence of the rhombohedral phase

Results of Rietveld analysis of the synchrotron XRD data on Pb(Zr_xTi_1-x)O_3 (PZT) for 0.525\leqx\leq0.60 are presented to show the absence of rhombohedral phase on the Zr-rich side of the morphotropic phase boundary (MPB). Our results reveal that the structure of PZT is monoclinic in the Cm space group for 0.525\leq x\leq 0.60. The nature of the monoclinic distortion changes from pseudo-tetragonal for 0.525\leqx\leq0.54 to pseudo-rhombohedral for x>0.54.Comment: 12 pages, 5 figur

Effect of lattice volume and strain on the conductivity of BaCeY-oxide ceramic proton conductors

In-situ electrochemical impedance spectroscopy was used to study the effect of lattice volume and strain on the proton conductivity of the yttrium-doped barium cerate proton conductor by applying the hydrostatic pressure up to 1.25 GPa. An increase from 0.62 eV to 0.73 eV in the activation energy of the bulk conductivity was found with increasing pressure during a unit cell volume change of 0.7%, confirming a previously suggested correlation between lattice volume and proton diffusivity in the crystal lattice. One strategy worth trying in the future development of the ceramic proton conductors could be to expand the lattice and potentially lower the activation energy under tensile strain

Site‐selective substitution and resulting magnetism in arc‐melted perovskite ATiO₃₋δ (A = Ca, Sr, Ba)

Magnetic properties in perovskite titanates ATiO₃₋δ (A = Ca, Sr, Ba) were investigated before and after arc melting. Crystal structure analysis was conducted by powder synchrotron X‐ray diffraction with Rietveld refinements. Quantitative chemical element analysis was carried out by X‐ray photoelectron spectroscopy. Magnetic measurements were conducted by vibrating sample magnetometer and X‐ray magnetic circular dichroism (XMCD). The magnetic properties are found to be affected by impurities of 3d elements such as Fe, Co, and Ni. Depending on the composition and crystal structure, the occupation of the magnetic ions in perovskite titanates is selectively varied, which is interpreted to be the origin of the different magnetic behaviors in arc‐melted perovskite titanates ATiO₃₋δ (A = Ca, Sr, Ba). In addition, both formation of oxygen vacancies and the reduction of Ti⁴⁺ to Ti³⁺ during arc‐melting also play a role as proven by XMCD. Nevertheless, preferential site occupation of magnetic impurities is dominant in the magnetic properties of arc‐melted perovskite ATiO₃₋δ (A = Ca, Sr, Ba)

Plasma-Enabled Process with Single-Atom Catalysts for Sustainable Plastic Waste Transformation.

In this study, we present a novel plasma-enabled strategy for the rapid breakdown of various types of plastic wastes, including mixtures, into high-value carbon nanomaterials and hydrogen. The H2 yield and selectivity achieved through the catalyst-free plasma-enabled strategy are 14.2 and 5.9 times higher, respectively, compared to those obtained with conventional thermal pyrolysis. It is noteworthy that this catalyst-free plasma alone approach yields a significantly higher energy yield of H2 (gH2/kWh) compared to other pyrolysis processes. By coupling plasma pyrolysis with thermal catalytic process, employing of 1 wt.% M/CeO2 atomically dispersed catalysts can further enhance hydrogen production. Specifically, the 1 wt.% Co/CeO2 catalyst demonstrated excellent catalytic performance throughout the 10 cycles of plastic waste decomposition, achieving the highest H2 yield of 46.7 mmol/gplastic (equivalent to 64.4% of theoretical H2 production) and nearly 100% hydrogen atom recovery efficiency at the 7th cycle. Notably, the H2 yield achieved over the atomically dispersed Fe on CeO2 surface in the integrated plasma-thermal catalytic process is comparable to that obtained with Fe particles on CeO2 surface (10 wt.%). This innovative and straightforward approach provides a promising and expedient strategy for continuously converting diverse plastic waste streams into high-value products conducive to a circular plastic economy

Resolving the characteristics of morphotropic phase boundary in the (1-x)Pb(Fe<SUB>1/2</SUB>Nb<SUB>1/2</SUB>)O<SUB>3</SUB>-xPbTiO<SUB>3</SUB> system: a combined dielectric and synchrotron x-ray diffraction study

Frequency dependent dielectric studies on the mixed system (1-x)Pb(Fe1/2Nb1/2)O3-xPbTiO3 reveal contributions from the electrodes, grain boundaries, and grains. It is shown that the intrinsic value of the dielectric permittivity coming only from the grains peaks at x=0.08. Analysis of synchrotron x-ray diffraction profiles using the Rietveld technique shows that this peaking is linked with a monoclinic to tetragonal morphotropic phase transition in the multiferroic system

Surfactant-free hydrothermal synthesis of highly tetragonal barium titanate nanowires: A structural investigation

Barium titanate nanowires synthesized with a surfactant-free hydrothermal method have been characterized by various techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), synchrotron X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The TEM and SEM analyses show the uniform cylindrical nanowires. The Rietveld refinement with synchrotron X-ray powder diffraction showed that the lattice parameters of cubic and tetragonal phases were a (= b = c) = 4.0134 angstrom and a (= b) = 3.9998 angstrom, c = 4.0303 angstrom, respectively. The final weighted R-factor, R-wp, was 6.75% and the goodness of fit indicator was 1.30. The mass fraction of tetragonal and cubic phases based on the refined scale factor for the two phases were 98.4% and 1.6%, respectively, which clearly show the nanowires are tetragonal. The XPS analysis has shown that as-obtained BaTiO3 nanowires were phase pure. The Raman spectra confirm the tetragonal phase of the BaTiO3 nanowires. The dielectric constant measurement shows the shift in the transition temperature (T-c = 105 degrees C) compared to the bulk transition temperature (T-c = 132 degrees C). The dielectric constant at T-c was 174 measured at 1 kHz frequencyclose75808

Evidence for monoclinic crystal structure and negative thermal expansion below magnetic transition temperature in Pb(Fe<SUB>1/2</SUB>Nb<SUB>1/2</SUB>)O<SUB>3</SUB>

The existing controversy about the room temperature structure of multiferroic Pb(Fe1/2Nb1/2)O3 is settled using synchrotron powder x-ray diffraction data. Results of Rietveld refinements in the temperature range of 300-12 K reveal that the structure remains monoclinic in the Cm space group down to 12 K, but the lattice parameters show anomalies at the magnetic transition temperature (TN) due to spin-lattice coupling. The lattice volume exhibits negative thermal expansion behavior, with a=-4.64&#215;10-6K-1, below TN