Search Results (5)

BaTiO₃-based lead-free ferroelectric films with a large recoverable energy density (W_rec) and a high energy efficiency (η) are crucial components for next-generation dielectric capacitors, which are used in energy conditioning and storage applications in integrated circuits. In this study, grain-engineered (Ba_0.95,Sr_0.05)(Zr_0.2,Ti_0.8)O₃ (BSZT) ferroelectric thick films (~500 nm) were prepared on Si substrates. These films were deposited at 350 °C, 100 °C lower than the temperature at which the LaNiO₃ buffer layer was deposited on Pt/Ti. This method reduced the (001) grain population due to a weakened interface growth mode, while promoting volume growth modes that produced (110) and (111) grains with a high polarizability. As a result, these films exhibited a maximum polarization of ~88.0 μC/cm², a large W_rec of ~203.7 J/cm³, and a high energy efficiency η of 81.2% (@ 6.4 MV/cm). The small-field dielectric constant nearly tripled as compared with that of the same BSZT/LaNiO₃ heterostructure deposited at the same temperature (350 °C or 450 °C). The enhanced linear dielectric response, delayed ferroelectric polarization saturation, and increased dielectric strength due to the nano-grain size, collectively contributed to the improved energy storage performance. This work provides a novel approach for fabricating high-performance dielectric capacitors for energy storage applications. Full article

Ferroelectric thin films with a high dielectric tunability (η) have great potential in electrically tunable applications, including microwave tunable devices such as phase shifters, filters, delay lines, etc. Using a modified Landau–Devonshire type thermodynamic potential, we show that the dielectric tunability η of a (001) tetragonal ferroelectric film can be analytically solved. After a survey of materials, a large η value above 60% was predicted to be achievable in a (001)-oriented tetragonal Pb(Zr_0.52Ti_0.48)O₃ (PZT) film. Experimentally, (001)-oriented PZT thin films were prepared on LaNiO₃-coated (100) SrTiO₃ substrates by using pulsed laser deposition (PLD). These films exhibited good dielectric tunability (η ~ 67.6%) measured at a small electric field E of ~250 kV/cm (corresponding to 5 volts for a 200 nm thick film). It only dropped down to ~54.2% when E was further reduced to 125 kV/cm (2.5 volts for 200 nm film). The measured dielectric tunability η as functions of the applied electric field E and measuring frequency f are discussed for a 500 nm thick PZT film, with the former well described by the theoretical η(E) curves and the latter showing a weak frequency dependence. These observations validate our integrated approach rooted in a theoretical understanding. Full article

AgNbO₃ antiferroelectric materials have become a hot topic due to their typical double polarization–electric field loops. AgNbO₃ films usually exhibit superior properties to bulks. In this work, AgNbO₃ films were fabricated via the pulsed laser deposition on (001) SrTiO₃ substrate with (La_0.5Sr_0.5)CoO₃, LaNiO₃ and SrRuO₃ bottom electrodes, in which the (La_0.5Sr_0.5)CoO₃, LaNiO₃ and SrRuO₃ bottom electrodes were used to regulate the in-plane compressive stress of AgNbO₃ films. It is found that AgNbO₃ films deposited on (La_0.5Sr_0.5)CoO₃, LaNiO₃ and SrRuO₃ bottom electrodes are epitaxial with dense microstructure. In changing the bottom electrodes from (La_0.5Sr_0.5)CoO₃, LaNiO₃ to SrRuO₃, the in-plane compressive stress of AgNbO₃ thin films becomes weaker, which leads to increased relative dielectric permittivity and reduced antiferroelectric–ferroelectric phase transition electric field E_F from 272 kV/cm to 190 kV/cm. The reduced E_F implies weakened antiferroelectric stability in AgNbO₃ films. It can be seen that the antiferroelectric stability of AgNbO₃ films could be regulated by changing the bottom electrodes. Full article

The control of the spontaneous formation of nanostructures at the surface of thin films is of strong interest in many different fields, from catalysts to microelectronics, because surface and interfacial properties may be substantially enhanced. Here, we analyze the formation of nickel oxide nanocuboids on top of La₂Ni_1−xMn_1+xO₆ double perovskite ferromagnetic thin films, epitaxially grown on SrTiO₃ (001) substrates by radio-frequency (RF) magnetron sputtering. We show that, by annealing the films at high temperature under high oxygen partial pressure, the spontaneous segregation of nanocuboids is enhanced. The evolution of the structural and magnetic properties of the films is studied as a function of the annealing treatments at different temperatures. It is shown that the formation of NiOx nanocuboids leads to a nanostructured film surface with regions of locally different electrical transport characteristics. Full article

The adsorption of H₂ on LaNiO₃ was investigated using density functional theory (DFT) calculations. The adsorption sites, adsorption energy, and electronic structure of LaNiO₃(001)/H₂ systems were calculated and indicated through the calculated surface energy that the (001) surface was the most stable surface. By looking at optimized structure, adsorption energy and dissociation energy, we found that there were three types of adsorption on the surface. First, H₂ molecules completely dissociate and then tend to bind with the O atoms, forming two –OH bonds. Second, H₂ molecules partially dissociate with the H atoms bonding to the same O atom to form one H₂O molecule. These two types are chemical adsorption modes; however, the physical adsorption of H₂ molecules can also occur. When analyzing the electron structure of the H₂O molecule formed by the partial dissociation of the H₂ molecule and the surface O atom, we found that the interaction between H₂O and the (001) surface was weaker, thus, H₂O was easier to separate from the surface to create an O vacancy. On the (001) surface, a supercell was constructed to accurately study the most stable adsorption site. The results from analyses of the charge population; electron localization function; and density of the states indicated that the dissociated H and O atoms form a typical covalent bond and that the interaction between the H₂ molecule and surface is mainly due to the overlap-hybridization among the H 1s, O 2s, and O 2p states. Therefore, the conductivity of LaNiO₃(001)/H₂ is stronger after adsorption and furthermore, the conductivity of the LaNiO₃ surface is better than that of the LaFeO₃ surface. Full article