Donor Doping Effect Research Articles

Enhancing the dielectric properties of polyimide-based composites with donor-doped SiO2

It is important that the dielectric material in the electrical system be able to handle the increasing applied electric strength owing to the rising demands for power supply reliability. Based on this, in this work, Nb2O5 donor doped SiO2 (NSO) particles were synthesized by high-temperature sintering method and successfully doped into the PI matrix. The maximum Eb of the composite material is 527.3 kV/mm, which is 64.2% higher than that of pure PI (321.1 kV/mm) and 34.8% higher than that of the SiO2/PI composite material (392.5 kV/mm) owning to the effect of donor doping on the carrier transport of the composite material. At the same time, it maintains excellent dielectric stability and lower dielectric loss even at 100 ℃. These consequences offer a new strategy for enhancing the integrated dielectric properties of polymer dielectrics in insulation fields.

Realization of high piezoelectric performance in bismuth titanate niobate via B-site mixed-valance doping

Aurivillius-compound Bi3TiNbO9 (BTN) based high-temperature piezoelectric ceramics doped with mixed-valence cations (Mo1/3Cr2/3)4+ at the lattice B-sites, Bi3Ti1−x(Mo1/3Cr2/3)xNbO9 (BTN-MC100x, x = 0 −0.07), were prepared via the solid-state reaction method. The incorporation of the (Mo1/3Cr2/3)4+ ions into the BTN lattice promotes the preferential growth of grains along the a-axis, making it easier for polarization vector to flip. The optimized composition BTN-MC5 ceramic had a large d33 of 20.3 pC/N with a high TC of 901 °C. It was found that the donor doping effect of (Mo1/3Cr2/3)4+ and the formation of (CrTi′–VO⋅⋅–CrTi′)×defect dipoles contribute to reduce the concentration of oxygen vacancies, thus increasing the resistivity (2.2 ×105 Ω cm at 600 °C). In addition, the d33 of the BTN-MC5 ceramic exhibits an excellent thermal stability against depoling temperature Td. These findings indicate that the BTN-MC5 ceramic is promising candidate for the preparation of high-temperature piezoelectric sensors.

Super-structured defects modulation for synergistically optimizing thermoelectric property in SnTe-based materials

Among the intriguing p-type thermoelectric IV-VI compounds, SnTe is an important alternative to both PbTe and GeTe for free of toxicity of Pb and scarcity of Ge. However, pristine SnTe has poor thermoelectric performance because of its intrinsic high hole concentration, big energy difference between L and Σ bands and high lattice thermal conductivity. In this work, In and Cd co-doping SnTe material, which combines the effect of resonant level and band convergence together, was obtained by self-propagating high-temperature synthesis (SHS) and plasma activated sintering (PAS). The generated Te vacancies are regularly arranged to form super-structured defects in the subsequent constrained hot compressing process, which include regular array of atomic defects and nanoscale precipitates. As a result, the hole concentration of the compressed SnTe-based material is reduced due to the donor doping effect of Te vacancies, and the hole mobility is remarkably improved to 372.94 cm2V−1s−1 and 66.19 cm2V−1s−1 at room temperature for the SnTe and In0.01Cd0.02Sn0.97Te material with compressibility of 35%, respectively. These atomic and nanoscale super-structured defects not only ensure superior electrical transport properties, but also bring much stronger scattering effect on phonons, thus leading to extremely low lattice thermal conductivity of 1.2 Wm−1K−1 at 888 K for the 35% compressed In0.01Cd0.02Sn0.97Te material. With synergistically optimized carrier and phonon transport behavior through resonant level engineering, band convergence engineering and super-structured defects engineering, a peak ZT value of 0.8 is achieved in In0.01Cd0.02Sn0.97Te material with compressibility of 35%. This work provides an effective strategy to realize the decoupling of electron and phonon scattering through Te vacancy-based super-structured defects modulation, and makes up an important part of multiscale microstructure tailoring for thermoelectric materials.

Combined effect of donor doping and RGO (reduced graphene oxide) coating in La/Nb-doped SrTiO3 thermoelectrics

SrTiO3 (STO) is one of the most promising oxide thermoelectric (TE) materials with high thermopower, but the low electrical conductivity and high thermal conductivity are still issues to be solved. Recently, grain boundary engineering using reduced graphene oxide (RGO) has been demonstrated to have capable of simultaneously improving both the electrical and thermal properties of STO. In this study, we investigated the combined effect of La/Nb doping and RGO coating in STO to improve further the electrical conductivity and the TE efficiency of STO materials. Two series of La- and Nb-doped Sr1-xLaxTi1-yNbyO3 (x, y = 0–0.02) samples incorporated with RGO were prepared by a combinatorial procedure of solid-state reaction, RGO coating, and the spark plasma sintering (SPS) process. The structural, morphological and temperature-dependent thermoelectric properties of the Sr1-xLaxTi1-yNbyO3/RGO were studied and as a result, the figure of merit was enhanced ∼6.5 times by the combined effect of donor doping and lowering the double Schottky barrier height due to RGO at grain boundaries.

The Effect of Donor Doping on the Ionic (О2–, Н+) Transport in Novel Complex Oxides BaLaIn1 – xNbxO4 + x with the Ruddlesden–Popper Structure

The Effect of Donor Doping on the Ionic (О2–, Н+) Transport in Novel Complex Oxides BaLaIn1 – xNbxO4 + x with the Ruddlesden–Popper Structure

Effect of Co doping on chemosorbed oxygen accumulation and gas response of SnO2 under dynamic program cooling

During the process of metal oxide semiconductors (MOS) gas sensing, the chemisorbed oxygen on the surface plays a significant important role, which determines the surface reactivity and controls the film conductivity. Therefore, it is necessary to improve the amount of chemisorbed oxygen on MOS surface. In this paper, the effect of doping on the accumulation of chemosorbed oxygen on SnO2 surface was studied. SnO2, Co-SnO2 and Nb-SnO2 were successfully synthesized via nonaqueous sol-gel method to study the effect of acceptor doping and donor doping on accumulation of chemosorbed oxygen and gas response. And dynamic program cooling (DPC) was also carried out in different concentrations of acetone and different gases respectively to obtain the R-T curve and gas response. The results showed that the Co doped SnO2 obviously improved the accumulation of chemosorbed oxygen and dynamic gas response, while the Nb doping has little improvement. The reason of these results was also analyzed by band theory in this paper.

Simultaneously Breaking the Double Schottky Barrier and Phonon Transport in SrTiO3-Based Thermoelectric Ceramics via Two-Step Reduction.

The low powder factor (PF) of polycrystalline oxide perovskites induced by the resistive grain boundaries or known as double Schottky barrier (DSB) greatly restricts their thermoelectric performance in application. Here, a general protocol including (i) powder and (ii) bulk reduction in H2/Ar forming gas is demonstrated to break the DSB in La and Nb codoped SrTiO3. While the powder reduction guarantees a high carrier concentration by fully stimulating the donor doping effect, the bulk reduction effectively lowers the DSB by influencing the point defects at grain boundaries, which is proved by the combination of cathode luminescence spectra and energy-dispersive X-ray spectroscopy in transmission electron microscopy. The Hall mobility can approach 10 cm2 V-1 s-1 after two-step reduction, which is similar to the level of single crystals. However, the Seebeck coefficient is not compromised, giving rise to high PF values up to 1.70 mW m-1 K-1 under proper reduction strength. Meanwhile, the reduction process also promotes mild precipitation of Nb nanoparticles, thus effectively lowering the lattice thermal conductivity by scattering phonons. As a result, a remarkable figure of merit reaching 0.4 at 700 K is obtained, which validates the two-step reduction as a reliable strategy toward "electron crystal-phonon glass" behavior in SrTiO3-based perovskites.

Effect of acceptor and donor doping on the state of protons in block-layered structures based on BaLaInO4

The present work describes the effect of acceptor and donor doping on the state of protons in block-layered proton conductors based on BaLaInO4. It was proved that the increase of the dopant concentration (both Ba2+ and Ti4+) leads to the increase of the amount of water uptake and at the same time to the decrease in the contribution of protons, involved in the strong H-bonds. The main factor determined the increase of concentration of protonic species is not the nature of appeared oxygen defects (oxygen vacancy or oxygen interstitial), but the increase in the unit cell volume during doping.

High-temperature energy storage performances in (1-x)(Na0.50Bi0.50TiO3)-xBaZrO3 lead-free relaxor ceramics

In this study, in order to obtain superior energy storage performances over a wide temperature range in lead-free dielectric ceramics, we develop and prepare (1-x)(Na0.50Bi0.50TiO3)-xBaZrO3 ((1-x)NBT-xBZ) relaxor ferroelectric ceramics by introducing BaZrO3 into Na0.50Bi0.50TiO3. BZ possesses small remnant polarization (Pr) and slim polarization-electric field (P-E) loops attributed to its room-temperature paraelectric phase structure characteristic. Thus, when it is added into NBT, the P-E loops of (1-x)NBT-xBZ ceramics are slimmer, and the Pr decreases. Besides, due to the donor doping effect resulting from the replacement of Ba2+ with higher valence for the Na+, with the increase of the BZ content, the grain sizes of the ceramics gradually decrease, resulting in the enhancement of the breakdown strength (Eb). All above these are in favour of improving energy storage properties, and as a result, by adjusting the BZ content reasonably, a large recoverable energy density (Wre) of 1.56 J/cm3 and high energy efficiency (η) of 80.56% are concurrently achieved in the 0.75NBT-0.25BZ ceramic. More interestingly, the ceramic exhibits excellent high-temperature energy storage capacity, which is superior to those of recently reported dielectric ceramics, and good fatigue properties. All these indicates that 0.75Na0.50Bi0.50TiO3-0.25BaZrO3 lead-free relaxor ferroelectric ceramic is a good candidate for preparing dielectric capacitors applicable in various environmental conditions.

Effect of ZnO doping on (K,Na)NbO3-based lead-free piezoceramics: Enhanced ferroelectric and piezoelectric performance

Potassium sodium niobate (KNN)-based materials are promising lead-free candidates for replacing lead zirconate titanate (PZT)-based piezoelectric materials. Chemical modification of KNN-based compositions has been a fundamental approach for achieving high performance. However, the understanding of donor doping and acceptor doping in KNN-based materials is still under-developed, compared to that in the PZT-based system. In the present study, we investigated the doping effect of ZnO on a KNN-based ceramic with the composition of 0.92(K0.5Na0.5)NbO3-0.02(Bi0.5Li0.5)TiO3-0.06BaZrO3. ZnO was found to exhibit donor doping effect, significantly enhancing the ferroelectricity and piezoelectricity, accompanied by a major contribution to the suppressed formation of oxygen vacancy. Optimized properties (d33 = 350 pC/N, d33∗ = 507 pm/V, Pr = 18.4 μC/cm2) were obtained in the sample with 0.3 wt% ZnO doping. The discovery of the donor doping of ZnO is important to the development of KNN-based piezoelectric materials as it provides a refreshing perspective on the defect chemistry of the KNN-based materials.

Composition-sensitive electrical properties of charge nonstoichiometric 0.94Bi0.5+xNa0.5−xTiO3–0.06BaTiO3 ceramics

Charge nonstoichiometric 0.94[Formula: see text][Formula: see text]TiO3–0.06BaTiO3 (BNT-BT) ([Formula: see text]) ceramics were prepared and investigated. The depolarization temperature was dependent on composition and the ferroelectric property of [Formula: see text] was suppressed more significantly than the [Formula: see text], indicating the composition-sensitive electrical properties. Furthermore, the [Formula: see text] was close to the insulator/conductor composition boundary while the [Formula: see text] was close to the ferroelectrics/relaxor boundary. These results were attributed to the complex effect of donor doping and acceptor doping on depolarization field. This work provides robust clues to tune and/or design electrical property and conductivity of [Formula: see text][Formula: see text]TiO3-based materials.

The impedance, dielectric and piezoelectric properties of Tb4O7 and Tm2O3 doped KNN ceramics

Rare earth (RE) elements (Tb, Tm) doped K0.5Na0.5NbO3 (KNN) lead-free ceramics were fabricated using conventional solid-state reaction method. All samples with dominating orthorhombic phase are well developed. The effects of Tb and Tm on impedance, dielectric and ferroelectric properties are systematically studied. There are relaxation-like features of the ceramics after the doping of RE elements. Conduction processes were affected by defect, especially in KNN-Tb ceramics, in the higher temperature region. The doping of Tb and Tm increases density, remnant polarization and the piezoelectric constant of the KNN ceramics due to the effect of donor doping. The overall analysis has confirmed the significance of RE elements (Tb, Tm) doping in KNN and shows that it is a promising candidate as lead-free piezoelectric ceramics.

Vertically-aligned lead-free BCTZY nanofibers with enhanced electrical properties for flexible piezoelectric nanogenerators

Flexible lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-0.2 mol%Y nanofibers (BCTZY NFs) were synthesized by electrospinning and their corresponding nanogenerators (NGs) with vertical alignments were fabricated. The low-temperature sintering properties of BCTZY NFs were investigated, to optimize their synthesis path and minimize the thermal energy consumption during the sintering process. The continuity, flexibility, and stability of the BCTZ-based NFs were improved by adding Y3+. Moreover, the temperature-evolved Raman spectra displayed a high Curie temperature of 280 °C for BCTZY NFs, which was far higher than that of about 90 °C for BCTZ-based ceramic bulks, owing to the discontinuous physical property of NFs. The dielectric, ferroelectric, and piezoelectric properties of the vertically aligned BCTZY NFs/PDMS were estimated and compared with those of BCTZ NFs/PDMS composites, to verify the advantages of vertical alignments and the donor doping effect of Y3+. Vertically aligned BCTZY NF-based NGs showed an average VOC of 3.0 V and ISC of 85 nA by finger tapping, suggesting their potential applications in tiny energy harvesting.

Exploration on the origin of enhanced piezoelectric properties in transition-metal ion doped KNN based lead-free ceramics

In this work, we studied effects of Ni2O3 and Co2O3 doping on crystal structures, microstructures, orthorhombic and tetragonal phase transition temperature (To-t), and electrical properties of [Li0.06(Na0.57K0.43)0.94][Ta0.05(Sb0.06Nb0.94)0.95]O3 (LNKTSN) lead-free ceramics. The experimental results showed that the Ni2O3 addition with appropriate amount could shift the To-t downwards to the room temperature, and thus obviously increasing the room-temperature piezoelectric coefficient (d33), dielectric coefficient (εr) and electromechanical coupling coefficient (kp) of the LNKTSN ceramics. These were consistent with previous experimental results obtained in Fe2O3 doped LNKTSN ceramics. On the contrary, Co3+ doping shifted continuously the To-t upward and deteriorated obviously piezoelectric properties of LNKTSN ceramics. Fe, Co and Ni had similar ion radii and were expected to result in the same (donor or acceptor) doping effects on electrical properties of LNKTSN ceramics. The different doping effects between Co3+ (deterioration) and Ni3+ or Fe3+ (improvement) on the electrical properties of LNKTSN ceramics suggested that the coexistence of orthorhombic and tetragonal phases at room temperature due to downward shift of To-t, rather than ion doping (donor or acceptor doping) effects was the main cause for enhanced room-temperature piezoelectric properties. This conclusion can be extended to all KNN-based materials in general, thus offering principle guide for future development of new lead-free materials with good piezoelectric properties.

Role of Cu and Y in sintering, phase transition, and electrical properties of BCZT lead-free piezoceramics

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-xwt%CuOywt%Y2O3 (BCZT-CuxYy) ceramics with high piezoelectricity were synthesized by the conventional solid-state reaction method. The role of Cu and Y (Cu/Y) in sintering, phase transition, and electrical properties of such ceramics was systematically studied. The results indicated that the sintering temperatures of BCZT-CuxYy decreased by at least 100 °C due to the low melting point of CuO. The promotion effect of Cu/Y on phase transition lied in the improvement of TC by 5–15 °C and the coexistence of O+T phase near room temperature. The contribution of Cu/Y to electrical properties was mainly ascribed to the grains growth, the formed oxygen vacancies and lattice distortions, and the donor doping effect of Y3+. Adding 0.10 wt% Cu2+ and 0.06 wt% Y3+ into BCZT dramatically improved the electrical properties as following: d33 = 552 pC/N, εm = 10175, εr = 4546, tanδ = 0.016, TC = 100 °C, kp = 0.475, Qm = 157.2, Pr = 10.82 μC/cm2 and EC = 2.33 kV/cm. A plausible mechanism was obtained to explain the reaction process and the favorable performances of BCZT-CuxYy. Co-doping Cu2+ and Y3+ into BCZT could be a promising method to improve and balance the sintering, phase transition, and electrical properties for potential practical applications of lead-free piezoceramics.

Improved piezoelectricity and luminescence of Er3+/Yb3+ co-doped (K, Na)NbO3 ceramics by microwave sintering

ABSTRACTYb2O3 doped (K,Na)NbO3-0.5% Er2O3 (KNNEr) ceramics with the composition around the morphotropic phase boundary was synthesized by microwave sintering. KNN co-doped Yb2O3/Er2O3 ceramics exhibited enhanced ferroelectric, piezoelectric properties owing to the donor doping effect. The optimal performance of d33 = 115 pC/N, kp = 0.37, ϵr = 620 and tanδ = 4.9% were obtained for the ceramics with the addition of 0.25 mol% Yb2O3. And the green and red up-conversion emission intensities of these ceramics excited under 980 nm increased with the increasing content of Yb2O3. The results suggest that the KNNEr-Yb2O3 ceramics have potential application as a multifunctional device by integrating its excellent electrical and luminescence properties.

Study of Electrical Properties and Luminescence of Conventional Furnace and Microwave-Sintered Er3+/Yb3+ Co-doped (K, Na)NbO3 Ceramics

Yb2O3 doped (K0.5Na0.5)NbO3–0.5% Er2O3 (KNNEr) ceramics were synthesized by microwave sintering. (K, Na)NbO3 co-doped Yb2O3/Er2O3 ceramic exhibited enhanced piezoelectric and ferroelectric properties owing to the donor doping effect. The optimal performances of d 33 = 115 pC/N, k p = 0.37, e r = 620 and tanδ = 4.9% were obtained for the ceramics with the addition of 0.25 mol% Yb2O3. The green and red up-conversion emission intensities of KNNEr ceramics excited under 980 nm increased with the increasing content of Yb2O3. The results indicated that the KNNEr-Yb2O3 ceramics have potential application of multifunctional device by combining its excellent luminescence and electrical properties.

Effects of donor doping and acceptor doping on rutile TiO2 particles for photocatalytic O2 evolution by water oxidation

Crystalline defects of photocatalyst particles may be considered to be the recombination center of photoexcited electrons and holes. In this study, we investigated the photocatalytic activity of cation-doped rutile TiO2 photocatalysts for O2 evolution from an aqueous silver nitrate solution under ultraviolet light irradiation. The photocatalytic activity of rutile TiO2 was enhanced by donor doping of Ta5+ and Nb5+ with a valence higher than that of Ti4+, regardless of increased density of electrons and Ti3+ species (an electron trapped in Ti4+ sites). Conversely, acceptor doping of lower valence cations such as In3+ and Ga3+ decreased photocatalytic activity for O2 evolution by water oxidation. The doping of equal valence cations such as Sn4+ and Ge4+ hardly changed the activity of non-doped TiO2. This study demonstrates that Ti3+ species, which is a crystalline defect, enhanced the photocatalytic activity of semiconductor oxides, for example rutile TiO2 with large crystalline size.

Donor doping of K0.5Na0.5NbO3 ceramics with strontium and its implications to grain size, phase composition and crystal structure

In this study, the particular effects of A-site donor doping, such as crystal-structure change, the secondary-phase formation and the grain-size decrease, in a lead-free piezoceramic material K0.5Na0.5NbO3 (KNN) doped with Sr2+, were investigated. Extended X-ray absorption fine structure (EXAFS) analyses proved that Sr occupies the perovskite A-sublattice, and locally modifies the KNN monoclinic structure to cubic. Introducing Sr into the A-sublattice, as well as accounting for the charge-compensating A-site vacancies in the starting composition, causes increasing lattice disorder and microstrain, as determined from a Rietveld refinement of the synchrotron X-ray diffraction data. Above 2% Sr the system segregates the A-site vacancies in a secondary phase in order to release the chemical pressure, as revealed by Raman spectroscopy. All these effects result in an increasing number of low-angle grain boundaries that limit the grain growth and finally lead to a significant grain-size decrease.

The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT).

The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La3+ donor-doped, Fe3+ acceptor-doped and La3+/Fe3+-co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.