Publications by Colleges and Departments (MSU - Bozeman)
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Item Poling effect and piezoelectric response in high-strain ferroelectric 0.70Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 crystal(2010) Chen, H.-Y.; Tu, Chi-Shun; Hung, C.-M.; Chien, R.R.; Schmidt, V. Hugo; Ku, C. -S.; Lee, H.-Y.In situ high-resolution synchrotron x-ray diffraction, dielectric permittivity, hysteresis loop, and polarization current, were used to investigate phase transitions of (211)-cut 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO30.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystal before and after an electric (E)(E) field poling. A rhombohedral (R)–tetragonal (T)–cubic transition sequence was observed upon zero-field heating in both unpoled and poled samples. Before the R–T transition takes place, an extra dielectric and polarization current anomalies near 365 K were observed in the poled sample due to a transition of polarization ordering. The direct piezoelectric coefficient d33d33 exhibits a rapid increase for poling at E=1.0–1.3kV/cmE=1.0–1.3 kV/cm, followed by an overpoling behavior. The increment of polarization ordering plays an important role while the high piezoelectric response builds up.Item Nanotwin and phase transformation in tetragonal Pb(Fe1/2Nb1/2)1-xTixO3 single crystal(2008) Tu, Chi-Shun; Tseng, C.-T.; Chien, R.R.; Schmidt, V. Hugo; Hsieh, C.-M.This work is a study of phase transformation in (001)-cut Pb(Fe1/2Nb1/2)1−xTixO3Pb(Fe1/2Nb1/2)1−xTixO3 (x=48%)(x=48%) single crystals by means of dielectric permittivity, domain structure, and in situ x-ray diffraction. A first-order T(TNT)-C(TNT)T(TNT)-C(TNT) phase transition was observed at the Curie temperature TC≅518KTC≅518 K upon zero-field heating. T, TNTTNT, and C are tetragonal, tetragonal nanotwin, and cubic phases, respectively. T(TNT)T(TNT) and C(TNT)C(TNT) indicate that minor TNTTNT domains reside in the T and C matrices. Nanotwins, which can cause broad diffraction peak, remain above TC≅518KTC≅518 K and give an average microscopic cubic symmetry in the polarizing microscopy. Colossal dielectric permittivity (>104)(>104) was observed above room temperature with strong frequency dispersion. This study suggests that nanotwins can play an important role in relaxor ferroelectric crystals while phase transition takes place. The Fe ion is a potential candidate as a BB-site dopant for enhancing dielectric permittivity.Item Field-induced intermediate orthorhombic phase in (110)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 single crystal(2008) Tu, Chi-Shun; Schmidt, V. Hugo; Chien, R.R.; Tsai, S H; Lee, S.-C.; Luo, H.Item Piezoelectric response and origin in (001) Pb(Mg1/3Nb2/3)0.70Ti0.30O3 crystal(2008) Tu, Chi-Shun; Hsieh, C.-M.; Schmidt, V. Hugo; Chien, R.R.; Luo, H.Converse and direct piezoelectric coefficients (dC33 and dD33) of (001)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 (PMN-30%PT) single crystals have been investigated as a function of poling electric (E) field. E-field-dependent domain structures were observed by using a polarizing microscope. Both dC33 and dD33 exhibit a rapid increase at E=1–2 kV/cm and reach maxima at E=2.5–4 kV/cm. This study suggests that polarization rotation from rhombohedral to monoclinic MA phases plays an important role while the high piezoelectric response builds up. Overpoling phenomenon evidenced by a sudden reduction in piezoelectric coefficient with increasing field is very sensitive to Ti content.Item Effect of diamagnetic barium substitution on magnetic and photovoltaic properties in multiferroic BiFeO3(2014) Hung, C.-M.; Tu, Chi-Shun; Xu, Zhe-Rui; Chang, L.-Y.; Schmidt, V. Hugo; Chien, R.R.; Chang, W.-C.Spontaneous magnetization and photovoltaic (PV) effects have been measured in (Bi1- x Ba x )FeO3-δ ceramics for x = 0.05, 0.10, and 0.15. The substitution of Ba2+ ion in the A site of the perovskite unit cell can effectively enhance the ferromagnetic magnetization. The heterostructure of indium tin oxide (ITO) film/(Bi1- x Ba x )FeO3-δ ceramic/Au film exhibits significant PV effects under illumination of λ = 405 nm. The PV responses decrease with increasing Ba concentration. The maximum power-conversion efficiency in the ITO/(Bi0.95Ba0.5)FeO2.95/Au can reach 0.006%. A theoretical model based on optically excited current in the depletion region between ITO film and (Bi1- x Ba x )FeO3-δ ceramics is used to describe the I-V characteristic, open-circuit voltage (V oc), and short-circuit current density (J sc) as a function of light intensity.Item Calcium-doping effects on photovoltaic response and structure in multiferroic BiFeO3 ceramics(2013) Tu, Chi-Shun; Hung, C.-M.; Xu, Zhe-Rui; Schmidt, V. Hugo; Ting, Yi; Chien, R.R.; Peng, Y.-T.; Anthoninappen, J.Photovoltaic (PV) effects, power-conversion efficiencies, and structures have been systematically measured in (Bi1− x Ca x )FeO3−δ ceramics for x = 0.05, 0.10, and 0.15. The heterostructures of indium tin oxide (ITO) film/(Bi1− x Ca x )FeO3−δ ceramics/Au film exhibit significant PV effects under illumination of λ = 405 nm. The maximum power-conversion efficiency in the ITO/(Bi0.90Ca0.10)FeO2.95 (BFO10C)/Au can reach 0.0072%, which is larger than 0.0025% observed in the graphene/polycrystalline BFO/Pt films [Zang et al., Appl. Phys. Lett. 99, 132904 (2011)]. A theoretical model based on optically excited current in the depletion region between ITO film and Ca-doped BFO ceramics is used to describe the I-V characteristic, open-circuit voltage, and short-circuit current density as a function of illumination intensity. This work suggests that the Ca-substitution can reduce the rhombohedral distortion and stabilize the single-phase structure.Item Origins of dielectric response and conductivity in (Bi1-xNdx)FeO3 multiferroic ceramics(2011) Tu, Chi-Shun; Yang, W.-C.; Schmidt, V. Hugo; Chien, R.R.The dielectric response and conductivity have been measured in (Bi1−x Nd x )FeO3 (x = 0.0 and 0.05) ceramics as functions of temperature and frequency. A one-dimensional across-barrier model with intrinsic barriers, B (in temperature units), every lattice constant, a, and extrinsic barriers, B + Δ, every distance, d, is introduced to describe the dielectric response and conductivity. The across-barrier hopping is responsible for the high-temperature conductivity and step-like dielectric relaxation in the region of 500–800 K. Good qualitative fits of dielectric dispersion and conductivity are obtained with d = 20–30 nm, B = 8400–8700 K (∼0.72–0.75 eV), and Δ = 2500 K (∼0.215 eV). The resistivity plot of scaled ρ" versus ρ' indicates a contribution of grain boundaries or internal defects to the conductivity.Item Phase coexistence and Mn-doping effect in lead-free ferroelectric (Na1/2Bi1/2)TiO3 crystals(2010) Tu, Chi-Shun; Huang, S.-H.; Ku, C. -S.; Lee, H.-Y.; Chien, R.R.; Schmidt, V. Hugo; Luo, H.Phase transformations of (001)-cut (Na1/2Bi1/2)TiO3 (NBT) and 1 at. % Mn-doped NBT (Mn-NBT) crystals have been investigated by means of dielectric permittivity, conventional x-ray diffraction (XRD), and high-resolution synchrotron XRD and reciprocal space mapping. An R−R+T−T−C transition sequence was observed in NBT and Mn-NBT upon zero-field heating. R, T, and C are rhombohedral, tetragonal, and cubic phases, respectively. R+T represents that the ferroelastic T phase coexists with the ferroelectric R phase. The Mn dopant can enhance dielectric response and reduce the dielectric loss in the high-temperature region due to the increased degree of ordering.Item Rapid piezoelectric response and origin in (001) Pb (In1/2Nb1/2)0.70Ti0.30O3 crystal(2009) Tu, Chi-Shun; Chien, R.R.; Lee, S.-C.; Schmidt, V. Hugo; Luo, H.Normal piezoelectric coefficient d33, domain structure, and x-ray diffraction of a (001)-cut Pb(In1/2Nb1/2)0.70Ti0.30O3 (PIN-30%PT) single crystal have been investigated as a function of poling electric (E) field. E-field-dependent domain structures were observed by using a polarizing microscope. Piezoelectric coefficient d33 exhibits a rapid increase at E=1–3 kV/cm and reaches a maximum of about 1200 pC/N near E=6 kV/cm. Structurald spacing and domain structure results suggest that polarization rotation from rhombohedral to monoclinic MA phases causes the high piezoelectric response. Overpoling phenomenon associated with a sudden reduction of d33 with increasing field was not evidenced.Item Thermal stability of Ba(Zr0.8-xCexY0.2)O2.9 ceramics in carbon dioxide(2009) Tu, Chi-Shun; Chien, R.R.; Schmidt, V. Hugo; Lee, S.-C.; Huang, C.-C.; Tsai, Chih-LongIn situx-ray diffraction spectra (25–1000 °C) have been measured as a function of temperature for proton-conducting Ba(Zr0.8−xCexY0.2)O2.9 (x=0.0–0.4)ceramics in CO2 atmosphere. Atomic vibrations before and after exposure to CO2 were obtained by using the micro-Raman scattering (150–1600 cm−1). Ba(Zr0.8Y0.2)O2.9 and Ba(Zr0.6Ce0.2Y0.2)O2.9 reveal a promising thermal stability in CO2 without apparent decomposition up to 1000 °C. However, Ba(Zr0.5Ce0.3Y0.2)O2.9 and Ba(Zr0.4Ce0.4Y0.2)O2.9 exhibit thermally stable below 550 °C and then proceed an obvious chemical decomposition of BaCO3 and Zr0.8−xCexY0.2O2 above 550 °C, which were clearly evidenced by the Raman vibrations of 1057 and 466 cm−1, respectively. A first-order orthorhombic-hexagonal structure transition was confirmed in BaCO3 in the region of 810–850 °C upon heating. This study suggests that the Ba(Zr0.8−xCexY0.2)O2.9ceramics with x≤0.2 are promising candidates for proton-conducting applications in CO2-containing environment.
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