Browsing by Author "Idzerda, Yves U."

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Large moments in bcc FexCoyMnz ternary alloy thin films
(2018-02) Snow, Ryan J.; Bhatkar, Harsh; N'Diaye, A. T.; Arenholz, E.; Idzerda, Yves U.
The elemental magnetic moments and the average atomic moment of 10-20 nm thick single crystal bcc (bct) FexCoyMnz films deposited on MgO(001) have been determined as a function of a broad range of compositions. Thin film epitaxy stabilized the bcc structure for 80% of the available ternary compositional space compared to only a 23% stability region for the bulk. The films that display ferromagnetism represent 60% of the available compositional possibilities compared to 25% for the bulk. A maximum average atomic moment of 3.25 +/- 0.3 mu(B)/atom was observed for a bcc Fe9Co62Mn29 film (well above the limit of the Slater-Pauling binary alloy curve of 2.45 mu(B)/atom). The FexCoyMnz ternary alloys that exhibit high moments can only be synthesized as ultrathin films since the bcc structure is not stable in the bulk for those compositions. Published by AIP Publishing.
Raman spectra and structural stability in B-site manganese doped (Bi0.5Na0.5)0.925Ba0.075TiO3 relaxor ferroelectric ceramics
(2015-11) Anthoniappen, J.; Tu, Chi-Shun; Chen, Pin-Yi; Chen, Cheng-Sao; Idzerda, Yves U.; Chiu, S.-J.
Soft X-ray absorption (XAS), transmission electron spectroscopy (TEM), Raman spectroscopy, and synchrotron XRD have been studied in B-site 0–2 mol% manganese (Mn) doped (Bi0.5Na0.5)0.925Ba0.075TiO3 (BN7.5BT) relaxor ferroelectric ceramics. High-resolution synchrotron XRD and TEM reveal two phase coexistence of rhombohedral R3c and tetragonal P4bm structures in 0 and 0.2%, and an orthorhombic structure in 1 and 2% Mn-doped BN7.5BT at room temperature. Raman spectra of 0% Mn reveal structural transition from two phase coexistence to tetragonal phase near 190 °C with a softening anomaly, while 0.2–2% Mn-doped BN7.5BT show softening behavior near 290 °C upon heating. Raman spectra and synchrotron XRD indicate that Mn doping can enhance structural thermal stability in BN7.5BT ceramics.
Raman vibrations, domain structures, and photovoltaic effects in A-site La-modified BiFeO 3 multiferroic ceramics
(2015) Tu, Chi-Shun; Chen, Cheng-Sao; Chen, Pin-Yi; Xu, Zhe-Rui; Idzerda, Yves U.; Schmidt, V. Hugo; Lyu, M.-Q.; Chan, T.-S.; Liu, C.-Y.
Micro‐Raman spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy (TEM), oxygen vacancies, synchrotron X‐ray absorption spectroscopy, magnetizations, optical band gaps, and photovoltaic (PV) effects have been studied in (Bi1−xLax)FeO3 (BFO100xL) ceramics for x = 0.0, 0.05, 0.10, and 0.15. XRD, Raman spectra, and TEM confirm a rhombohedral R3c symmetry with the tilted FeO6 oxygen octahedra in all compounds. The low‐frequency Raman vibrations become broader and shift toward higher frequency as La3+ increases. Fe K‐edge synchrotron X‐ray absorptions reveal that Fe3+ valence and Fe–O–Fe bond angle are not modified by the La3+ substitution. All compounds exhibit a linear antiferromagnetic feature. Optical transmission reveals band gaps in the range of 2.22–2.24 eV. The heterostructures of indium tin oxide (ITO) film/(Bi1−xLax)FeO3 ceramics/Au film show a p–n junction‐like I–V characteristic behavior. The maximal PV power conversion efficiency can reach 0.19% in ITO/BFO15L/Au under illumination of λ = 405 nm. A junction‐like theoretical model can reasonably describe open‐circuit voltage and short‐circuit current as a function of illumination intensity.