Mojtaba Rahimabady - Academia.edu (original) (raw)

Papers by Mojtaba Rahimabady

Universitat de Girona. Càtedra Ferrater Mora, Oct 15, 2008

Applied Physics Letters, 2013

A nonlinear dielectric poly(vinylidene fluoride-co-hexafluoropropylene)-graft-poly(dopamine metha... more A nonlinear dielectric poly(vinylidene fluoride-co-hexafluoropropylene)-graft-poly(dopamine methacrylamide) [P(VDF-HFP)-g-PDMA] graft copolymer with ultra-high energy density of 33 J/cm3 was obtained by thermally initiated radical graft polymerization. It was observed that the dielectric constant of the graft copolymer films was 63% higher than that of P(VDF-HFP), with a large dielectric breakdown strength (>850 MV/m). Theoretical analyses and experimental measurements showed that the significant improvement in the electric polarization was attributed to the introduction of the highly polarizable hydroxyl groups in the PDMA side chains, and the large breakdown strength arose from the strong adhesion bonding of the catechol-containing graft copolymer to the metal electrode.

Journal of Applied Polymer Science

Sensors and Actuators B: Chemical

Journal of Advanced Dielectrics, 2014

Multilayer dielectric capacitors were fabricated from nanocomposite precursor comprised of BaTiO ... more Multilayer dielectric capacitors were fabricated from nanocomposite precursor comprised of BaTiO 3@ TiO 2 core–shell nanosized particles and poly(vinylidene fluoride–hexafluoropropylene) (P(VDF–HFP)) polymer matrix (20 vol%). The multilayer capacitors showed very high discharge speed and high discharged energy density of around 2.5 J/cm3 at its breakdown field (~ 166 MV/m). The energy density of the nanocomposite multilayer capacitors was substantially higher than the energy density of commercially used power capacitors. Low cost, flexible structure, high discharge rate and energy density suggest that the nanocomposite multilayer capacitors are promising for energy storage applications in many power devices and systems.

Thin Solid Films, 2008

100)-oriented 0.462Pb(Zn 1/3 Nb 2/3 )O 3 -0.308Pb(Mg 1/3 Nb 2/3 )O 3 -0.23PbTiO 3 (PZN-PMN-PT) pe... more 100)-oriented 0.462Pb(Zn 1/3 Nb 2/3 )O 3 -0.308Pb(Mg 1/3 Nb 2/3 )O 3 -0.23PbTiO 3 (PZN-PMN-PT) perovskite ferroelectric thin films were prepared on La 0.7 Sr 0.3 MnO 3 /LaAlO 3 (LSMO/LAO) substrate via a chemical solution deposition route. The perovskite LSMO electrode was found to effectively suppress the pyrochlore phase while promote the growth of the perovskite phase in the PZN-PMN-PT film. The film annealed at 700°C exhibited a high dielectric constant of 2130 at 1 kHz, a remnant polarization, 2P r , of 29.8 μC/cm 2 , and a low leakage current density of 7.2 × 10 − 7 A/cm 2 at an applied field of 200 kV/cm. The ferroelectric polarization was fatigue-free at least up to 10 10 cycles. Piezoelectric coefficient, d 33 , of 48 pm/V was also demonstrated. The results showed that much superior properties could be achieved with the PZN-PMN-PT thin films on the solution derived LSMO electrode than on Pt electrode by sputtering.

Thin Solid Films, 2010

The residual stress and its evolution with time in poly(vinylidene-fluoride-co-trifluoroethylene)... more The residual stress and its evolution with time in poly(vinylidene-fluoride-co-trifluoroethylene) (P(VDF-TrFE) (72/28)) piezoelectric polymer thin films deposited on silicon wafers were investigated using the wafer curvature method. Double-side polished silicon wafers with minimized initial wafer warpage were used to replace single-side polished silicon wafers to obtain significantly improved reliability for the measurement of the low residual stress in the P(VDF-TrFE) polymer thin films. Our measurement results showed that all the P(VDF-TrFE) films possessed a tensile residual stress, and the residual stress slowly decreased with time. Our analysis further indicates that the tensile stress could arise from the thermal mismatch between the P(VDF-TrFE) film and the silicon substrate. Besides possible viscoelastic creep mechanism in thermoplastic P(VDF-TrFE) films, microcracks with widths in the range of tens of nanometers appeared to release the tensile residual stress.

Physical chemistry chemical physics : PCCP, Jan 14, 2013

Nanocomposites comprising a P(VDF-HFP) polymer matrix and core-shell structured nanoparticle fill... more Nanocomposites comprising a P(VDF-HFP) polymer matrix and core-shell structured nanoparticle fillers were prepared, in which a crystalline, ultrathin TiO2 shell layer encapsulates BaTiO3 nanoparticles. A large dielectric constant (>110) was obtained, which was unexpectedly more than 3 times higher than that of the nanocomposite without the TiO2 shell layer. The significant improvement in electric polarization is attributed to the highly interactive interfaces among the multiple dielectric materials with the introduction of the intermediate TiO2 layer, which also improves the breakdown field (>340 MV m(-1)). Thus a resulting dielectric energy density of 12.2 J cm(-3) is achieved, among the highest energy densities for polymer-ceramic composites.

Journal of Applied Polymer Science, 2010

Poly(vinylidene fluoride) (PVDF) and copolymers of vinylidene fluoride and trifluoroethylene [P(V... more Poly(vinylidene fluoride) (PVDF) and copolymers of vinylidene fluoride and trifluoroethylene [P(VDF/ TrFE)s] were deposited on silicon substrates, and their structure and properties were comparatively investigated. Compared to P(VDF/TrFE), which is the polymer material currently most dominant for ferroelectric thin-film devices applications, our b-phase PVDF homopolymer thin film demonstrated several advantages, such as higher dielectric breakdown strength, improved polarization fatigue endurance, and larger ferroelectric polarization at elevated temperatures with improved thermal stability. The reasons for the observed different characteristics between the PVDF and P(VDF/TrFE) thin films were analyzed on the basis of their different structures and morphologies. The results indicate that the low-cost b-phase PVDF homopolymer thin films have great potential as an alternative to P(VDF/TrFE) for ferroelectric and piezoelectric thin-film-device applications.

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000

Although batteries possess high energy storage density, their output power is limited by the slow... more Although batteries possess high energy storage density, their output power is limited by the slow movement of charge carriers, and thus capacitors are often required to deliver high power output. Dielectric capacitors have high power density with fast discharge rate, but their energy density is typically much lower than electrochemical supercapacitors. Increasing the energy density of dielectric materials is highly desired to extend their applications in many emerging power system applications. In this paper, we review the mechanisms and major characteristics of electric energy storage with electrochemical supercapacitors and dielectric capacitors. Three types of in-house-produced ferroic nonlinear dielectric thin film materials with high energy density are described, including (Pb 0.97 La 0.02 )(Zr 0.90 Sn 0.05 Ti 0.

Ceramics International, 2009

Perovskite ferroelectric oxide ceramics of 0.1Pb) with excess MgO and NiO were investigated in th... more Perovskite ferroelectric oxide ceramics of 0.1Pb) with excess MgO and NiO were investigated in this work. The effects of the excess MgO and NiO doping on the ceramic structure, density, dielectric, ferroelectric and piezoelectric properties were studied. The chemical states of nickel were examined using X-ray photoelectron spectroscopy (XPS). Both XPS experimental results and theoretical analyses on the basis of ionic packing indicated that the excess valence-two ions substituted the A-sites in the ABO 3 perovskite structure. By completely eliminating the pyrochlore phase and enhancing densification with the excess NiO and MgO, improved piezoelectric coefficient d 33 up to 459 pC/N, higher ferroelectric remnant polarization and dielectric constant were demonstrated when sintered at temperature as low as 850-950 8C. #

Applied Physics Letters, 2013

Applied Physics Letters, 2011

Dense α-phase blend films of vinylidene fluoride (VDF) oligomer and poly (vinylidene fluoride)(PV... more Dense α-phase blend films of vinylidene fluoride (VDF) oligomer and poly (vinylidene fluoride)(PVDF) of various compositions were prepared from chemical solution deposition. The dielectric constant of the films was unexpectedly lower, and the mechanical strength ...

Applied Physics Letters, 2012

ABSTRACT Homogeneous poly(vinylidene fluoride-hexafluoropropylene) and poly (vinylidene fluoride)... more ABSTRACT Homogeneous poly(vinylidene fluoride-hexafluoropropylene) and poly (vinylidene fluoride) (P(VDF-HFP)/PVDF) blend films were prepared via a chemical solution approach, followed by quenching, annealing, and hot pressing. The intermolecular interactions of the blends were investigated through atomic simulation. Higher melting temperature, higher crystallinity, larger elastic modulus, and improved breakdown strength (>850 MV/m) were observed in the optimized polymer blends, in comparison with either of the two constituent polymers, PVDF or P(VDF-HFP). In addition, the P(VDF-HFP)/PVDF blend film also showed larger dielectric constant. As a result, an extremely high energy density of 30.1 J/cm3 was achieved in P(VDF-HFP)/PVDF (50:50 by weight) blend films.

Advanced Materials, 2010

While silicon-based diodes have been the dominant solar cell type, novel photovoltaic mechanisms ... more While silicon-based diodes have been the dominant solar cell type, novel photovoltaic mechanisms are being explored in pursuit of lower cost or improved efficiency. In a semiconductor photodiode, such as a Si solar cell, photons with energy higher than the band gap are absorbed to produce electron-hole pairs, which are separated by the internal field in the p-n junction and collected with the electrodes. However, a p-n junction is not a prerequisite for the photovoltaic effect. For exitonic solar cells, photon absorption creates excitons, which dissociate at a heterojunction. In materials without a center of symmetry, such as ferroelectric materials, steady-state photocurrent can exist in a homogeneous medium under uniform illumination, a phenomenon called bulk photovoltaic effect (BPVE). BPVE is a fascinating mechanism with many unique features such as extremely large photovoltage, a photocurrent proportional to the polarization magnitude, and charge-carrier separation in homogeneous media. Observed in bulk ferroelectrics in as early as 1950s, BPVE has seen a resurgent interest recently, especially in ferroelectric thin films. It has been proposed that remarkably higher photovoltaic efficiency can be achieved in thin films. On the other hand, open-circuit voltage much larger than the band gap has also been achieved with ferroelectric thin films with in-plane interdigital electrodes, which has led to the development of UV sensors and dosimeters. The ferroelectric thin-film materials under the previous study, such as BaTiO 3 and Pb(ZrTi)O 3 , have wide band gaps (typically larger than 3.3 eV) corresponding to the UV region. BPVE in visible wavelength could lead to the development of new photovoltaic cells or other novel optoelectronic devices. BiFeO 3 (BFO), a multiferroic material at room temperature with a band gap near 2.74 eV and a very large remnant ferroelectric polarization, offers a unique opportunity for such an investigation. Appreciable photoconductivity in visible light has been reported in BFO. Optical studies by absorption spectroscopy and spectroscopic ellipsometry have shown that BFO has a direct band gap with high absorption coefficient. Recently, a switchable-diode effect and a visible-light photovoltaic effect has been observed in BFO bulk crystals. However, no value of photovoltage has been reported for BFO single crystals and significant bulk photovoltaic response has not been demonstrated in BFO thin film. It is also unclear if the photovoltaic response in BFO is due to the diode effect. Here, we studied the photovoltaic effect in epitaxial BFO thin films and obtained an open-circuit voltage V oc of 0.3 V. We further demonstrated that photocurrent direction can be switched by the polarization direction of the BFO film and that the ferroelectric polarization is the main driving force of the observed photovoltaic effect. Moreover, the as-deposited BFO films were self-polarized and they could readily function as a photovoltaic cell without any poling.

Universitat de Girona. Càtedra Ferrater Mora, Oct 15, 2008

Applied Physics Letters, 2013

A nonlinear dielectric poly(vinylidene fluoride-co-hexafluoropropylene)-graft-poly(dopamine metha... more A nonlinear dielectric poly(vinylidene fluoride-co-hexafluoropropylene)-graft-poly(dopamine methacrylamide) [P(VDF-HFP)-g-PDMA] graft copolymer with ultra-high energy density of 33 J/cm3 was obtained by thermally initiated radical graft polymerization. It was observed that the dielectric constant of the graft copolymer films was 63% higher than that of P(VDF-HFP), with a large dielectric breakdown strength (>850 MV/m). Theoretical analyses and experimental measurements showed that the significant improvement in the electric polarization was attributed to the introduction of the highly polarizable hydroxyl groups in the PDMA side chains, and the large breakdown strength arose from the strong adhesion bonding of the catechol-containing graft copolymer to the metal electrode.

Journal of Applied Polymer Science

Sensors and Actuators B: Chemical

Journal of Advanced Dielectrics, 2014

Multilayer dielectric capacitors were fabricated from nanocomposite precursor comprised of BaTiO ... more Multilayer dielectric capacitors were fabricated from nanocomposite precursor comprised of BaTiO 3@ TiO 2 core–shell nanosized particles and poly(vinylidene fluoride–hexafluoropropylene) (P(VDF–HFP)) polymer matrix (20 vol%). The multilayer capacitors showed very high discharge speed and high discharged energy density of around 2.5 J/cm3 at its breakdown field (~ 166 MV/m). The energy density of the nanocomposite multilayer capacitors was substantially higher than the energy density of commercially used power capacitors. Low cost, flexible structure, high discharge rate and energy density suggest that the nanocomposite multilayer capacitors are promising for energy storage applications in many power devices and systems.

Thin Solid Films, 2008

100)-oriented 0.462Pb(Zn 1/3 Nb 2/3 )O 3 -0.308Pb(Mg 1/3 Nb 2/3 )O 3 -0.23PbTiO 3 (PZN-PMN-PT) pe... more 100)-oriented 0.462Pb(Zn 1/3 Nb 2/3 )O 3 -0.308Pb(Mg 1/3 Nb 2/3 )O 3 -0.23PbTiO 3 (PZN-PMN-PT) perovskite ferroelectric thin films were prepared on La 0.7 Sr 0.3 MnO 3 /LaAlO 3 (LSMO/LAO) substrate via a chemical solution deposition route. The perovskite LSMO electrode was found to effectively suppress the pyrochlore phase while promote the growth of the perovskite phase in the PZN-PMN-PT film. The film annealed at 700°C exhibited a high dielectric constant of 2130 at 1 kHz, a remnant polarization, 2P r , of 29.8 μC/cm 2 , and a low leakage current density of 7.2 × 10 − 7 A/cm 2 at an applied field of 200 kV/cm. The ferroelectric polarization was fatigue-free at least up to 10 10 cycles. Piezoelectric coefficient, d 33 , of 48 pm/V was also demonstrated. The results showed that much superior properties could be achieved with the PZN-PMN-PT thin films on the solution derived LSMO electrode than on Pt electrode by sputtering.

Thin Solid Films, 2010

The residual stress and its evolution with time in poly(vinylidene-fluoride-co-trifluoroethylene)... more The residual stress and its evolution with time in poly(vinylidene-fluoride-co-trifluoroethylene) (P(VDF-TrFE) (72/28)) piezoelectric polymer thin films deposited on silicon wafers were investigated using the wafer curvature method. Double-side polished silicon wafers with minimized initial wafer warpage were used to replace single-side polished silicon wafers to obtain significantly improved reliability for the measurement of the low residual stress in the P(VDF-TrFE) polymer thin films. Our measurement results showed that all the P(VDF-TrFE) films possessed a tensile residual stress, and the residual stress slowly decreased with time. Our analysis further indicates that the tensile stress could arise from the thermal mismatch between the P(VDF-TrFE) film and the silicon substrate. Besides possible viscoelastic creep mechanism in thermoplastic P(VDF-TrFE) films, microcracks with widths in the range of tens of nanometers appeared to release the tensile residual stress.

Physical chemistry chemical physics : PCCP, Jan 14, 2013

Nanocomposites comprising a P(VDF-HFP) polymer matrix and core-shell structured nanoparticle fill... more Nanocomposites comprising a P(VDF-HFP) polymer matrix and core-shell structured nanoparticle fillers were prepared, in which a crystalline, ultrathin TiO2 shell layer encapsulates BaTiO3 nanoparticles. A large dielectric constant (>110) was obtained, which was unexpectedly more than 3 times higher than that of the nanocomposite without the TiO2 shell layer. The significant improvement in electric polarization is attributed to the highly interactive interfaces among the multiple dielectric materials with the introduction of the intermediate TiO2 layer, which also improves the breakdown field (>340 MV m(-1)). Thus a resulting dielectric energy density of 12.2 J cm(-3) is achieved, among the highest energy densities for polymer-ceramic composites.

Journal of Applied Polymer Science, 2010

Poly(vinylidene fluoride) (PVDF) and copolymers of vinylidene fluoride and trifluoroethylene [P(V... more Poly(vinylidene fluoride) (PVDF) and copolymers of vinylidene fluoride and trifluoroethylene [P(VDF/ TrFE)s] were deposited on silicon substrates, and their structure and properties were comparatively investigated. Compared to P(VDF/TrFE), which is the polymer material currently most dominant for ferroelectric thin-film devices applications, our b-phase PVDF homopolymer thin film demonstrated several advantages, such as higher dielectric breakdown strength, improved polarization fatigue endurance, and larger ferroelectric polarization at elevated temperatures with improved thermal stability. The reasons for the observed different characteristics between the PVDF and P(VDF/TrFE) thin films were analyzed on the basis of their different structures and morphologies. The results indicate that the low-cost b-phase PVDF homopolymer thin films have great potential as an alternative to P(VDF/TrFE) for ferroelectric and piezoelectric thin-film-device applications.

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000

Although batteries possess high energy storage density, their output power is limited by the slow... more Although batteries possess high energy storage density, their output power is limited by the slow movement of charge carriers, and thus capacitors are often required to deliver high power output. Dielectric capacitors have high power density with fast discharge rate, but their energy density is typically much lower than electrochemical supercapacitors. Increasing the energy density of dielectric materials is highly desired to extend their applications in many emerging power system applications. In this paper, we review the mechanisms and major characteristics of electric energy storage with electrochemical supercapacitors and dielectric capacitors. Three types of in-house-produced ferroic nonlinear dielectric thin film materials with high energy density are described, including (Pb 0.97 La 0.02 )(Zr 0.90 Sn 0.05 Ti 0.

Ceramics International, 2009

Perovskite ferroelectric oxide ceramics of 0.1Pb) with excess MgO and NiO were investigated in th... more Perovskite ferroelectric oxide ceramics of 0.1Pb) with excess MgO and NiO were investigated in this work. The effects of the excess MgO and NiO doping on the ceramic structure, density, dielectric, ferroelectric and piezoelectric properties were studied. The chemical states of nickel were examined using X-ray photoelectron spectroscopy (XPS). Both XPS experimental results and theoretical analyses on the basis of ionic packing indicated that the excess valence-two ions substituted the A-sites in the ABO 3 perovskite structure. By completely eliminating the pyrochlore phase and enhancing densification with the excess NiO and MgO, improved piezoelectric coefficient d 33 up to 459 pC/N, higher ferroelectric remnant polarization and dielectric constant were demonstrated when sintered at temperature as low as 850-950 8C. #

Applied Physics Letters, 2013

Applied Physics Letters, 2011

Dense α-phase blend films of vinylidene fluoride (VDF) oligomer and poly (vinylidene fluoride)(PV... more Dense α-phase blend films of vinylidene fluoride (VDF) oligomer and poly (vinylidene fluoride)(PVDF) of various compositions were prepared from chemical solution deposition. The dielectric constant of the films was unexpectedly lower, and the mechanical strength ...

Applied Physics Letters, 2012

ABSTRACT Homogeneous poly(vinylidene fluoride-hexafluoropropylene) and poly (vinylidene fluoride)... more ABSTRACT Homogeneous poly(vinylidene fluoride-hexafluoropropylene) and poly (vinylidene fluoride) (P(VDF-HFP)/PVDF) blend films were prepared via a chemical solution approach, followed by quenching, annealing, and hot pressing. The intermolecular interactions of the blends were investigated through atomic simulation. Higher melting temperature, higher crystallinity, larger elastic modulus, and improved breakdown strength (>850 MV/m) were observed in the optimized polymer blends, in comparison with either of the two constituent polymers, PVDF or P(VDF-HFP). In addition, the P(VDF-HFP)/PVDF blend film also showed larger dielectric constant. As a result, an extremely high energy density of 30.1 J/cm3 was achieved in P(VDF-HFP)/PVDF (50:50 by weight) blend films.

Advanced Materials, 2010

While silicon-based diodes have been the dominant solar cell type, novel photovoltaic mechanisms ... more While silicon-based diodes have been the dominant solar cell type, novel photovoltaic mechanisms are being explored in pursuit of lower cost or improved efficiency. In a semiconductor photodiode, such as a Si solar cell, photons with energy higher than the band gap are absorbed to produce electron-hole pairs, which are separated by the internal field in the p-n junction and collected with the electrodes. However, a p-n junction is not a prerequisite for the photovoltaic effect. For exitonic solar cells, photon absorption creates excitons, which dissociate at a heterojunction. In materials without a center of symmetry, such as ferroelectric materials, steady-state photocurrent can exist in a homogeneous medium under uniform illumination, a phenomenon called bulk photovoltaic effect (BPVE). BPVE is a fascinating mechanism with many unique features such as extremely large photovoltage, a photocurrent proportional to the polarization magnitude, and charge-carrier separation in homogeneous media. Observed in bulk ferroelectrics in as early as 1950s, BPVE has seen a resurgent interest recently, especially in ferroelectric thin films. It has been proposed that remarkably higher photovoltaic efficiency can be achieved in thin films. On the other hand, open-circuit voltage much larger than the band gap has also been achieved with ferroelectric thin films with in-plane interdigital electrodes, which has led to the development of UV sensors and dosimeters. The ferroelectric thin-film materials under the previous study, such as BaTiO 3 and Pb(ZrTi)O 3 , have wide band gaps (typically larger than 3.3 eV) corresponding to the UV region. BPVE in visible wavelength could lead to the development of new photovoltaic cells or other novel optoelectronic devices. BiFeO 3 (BFO), a multiferroic material at room temperature with a band gap near 2.74 eV and a very large remnant ferroelectric polarization, offers a unique opportunity for such an investigation. Appreciable photoconductivity in visible light has been reported in BFO. Optical studies by absorption spectroscopy and spectroscopic ellipsometry have shown that BFO has a direct band gap with high absorption coefficient. Recently, a switchable-diode effect and a visible-light photovoltaic effect has been observed in BFO bulk crystals. However, no value of photovoltage has been reported for BFO single crystals and significant bulk photovoltaic response has not been demonstrated in BFO thin film. It is also unclear if the photovoltaic response in BFO is due to the diode effect. Here, we studied the photovoltaic effect in epitaxial BFO thin films and obtained an open-circuit voltage V oc of 0.3 V. We further demonstrated that photocurrent direction can be switched by the polarization direction of the BFO film and that the ferroelectric polarization is the main driving force of the observed photovoltaic effect. Moreover, the as-deposited BFO films were self-polarized and they could readily function as a photovoltaic cell without any poling.