Rotation Of Oxygen Octahedron Research Articles

Ferromagnetism with Strong Perpendicular Magnetic Anisotropy in Epitaxial SrMn0.3Ir0.7O3 Perovskite Films

Strong Coulomb repulsion and spin-orbit coupling are known to give rise to exotic physical phenomena in transition metal oxides. Here, we report magnetic characteristics of a ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_{3}$ perovskite thin film, having both 3d and 5d elements on the $B$ sites, with a strong perpendicular magnetic anisotropy (PMA), which is rare in perovskite oxide thin films. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_{3}$ films have been epitaxially deposited on (001)-oriented ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ single-crystal substrates by pulsed-laser deposition, exhibiting a para-to-ferromagnetic transition at about 110 K. The average valence of $\mathrm{Mn}$ and $\mathrm{Ir}$ cations are estimated as +3.61 and +4.17, respectively, by x-ray photoelectron spectroscopy. X-ray absorption spectroscopy reveals that $\mathrm{Mn}$ ${e}_{g}$ electrons occupy preferentially the ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital, which produces the observed PMA in the framework of spin-orbital coupling. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_{3}$ thin film shows a large effective anisotropy constant of about 1.2 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ erg ${\mathrm{cm}}^{\ensuremath{-}3}$ at 10 K, which is found to decrease with decreasing tetragonality c/a of the film. First-principles calculations reveal that $\mathrm{Mn}$ and $\mathrm{Ir}$ cations provide opposite magnetizations in ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_{3}$ and the $\mathrm{Mn}$ ${e}_{g}$ orbital polarization comes from both lattice distortion and oxygen octahedron rotation. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_{3}$ thin film with strong PMA may have applications in future low-power-consumption oxide spintronic devices.

Phase transitions and ferroelectricity of perovskite layered Sr2Nb2O7 ceramics

Spontaneous polarization (Ps) is the fundamental for ferroelectrics. Compared with the relative explicit origin of Ps of perovskite ferroelectrics and bismuth layer structured ferroelectrics, that of the perovskite layer structured ferroelectrics (PLSFs) is still unclear and controversial due to their unique layer structures. Sr2Nb2O7 compound with a high Curie temperature of 1342 °C is a typical representative in the family of PLSFs. Here, we report our investigations about the phase transitions and the mechanism of ferroelectricity of Sr2Nb2O7 ceramics from the viewpoint of layered crystal structure experimentally and theoretically. Sr2Nb2O7 has two phase transitions at about 215 °C and 1340 °C. Selected area electron diffraction (SAED) images show superlattice along the [001] zone axis related to an incommensurate modulation and confirm it's incommensurate-commensurate phase transition at around 215 °C. The latter on at 1340 °C corresponds to the paraelectric-ferroelectric phase transition which is originated from oxygen octahedral rotation along c-axis, named a0b0c+ in Glazer's notation. Phonon spectra shows the origin of Ps for Sr2Nb2O7 is from mainly the oxygen octahedral rotations and partially the displacement of Sr2+ ions. This study not only demonstrates the rotation of oxygen octahedron is the domination that affects ferroelectric polarization but also opens up a new direction to design high ferroelectric and piezoelectric PLSF ceramics.

Structural evolution and phase transition of Sr3Sn2O7 doped with Ca

The ceramics of Sr3-xCaxSn2O7 (x = 0,0.1,0.2,0.3,0.6,0.8,1) were synthesized by solid-state reaction method. The lattice constants of Sr3-xCaxSn2O7 decrease, and the rotation of oxygen octahedron around c axis increases with the increasing of Ca doping. The phase transition temperature of Sr3-xCaxSn2O7 increases 183.3 K with the increase of Ca doping concentration from × = 0 to × = 0.3. The space group of Sr3Sn2O7 changed from A21am to I4/mmm at 407.9 K. Near the phase transition temperature, the Raman shift of phonon mode A1(2) of Sr3-xCaxSn2O7 changes abruptly, and the phonon mode A2(2) disappears gradually.

Enhancement in hybrid improper ferroelectricity of Ca3Ti2O7 ceramics by a two-stage sintering

Ca3Ti2O7 ceramics were prepared by a solid-state reaction process, and the influences of the sintering process on its microstructure and electric properties have been systematically studied. All the ceramic samples fabricated by different sintering processes are single polar A21am phase at room temperature, and the results indicate that the extra calcining or sintering at 1400 °C is beneficial to get the higher lattice constants. Especially the Ca3Ti2O7 ceramics fabricated by the two-stage sintering exhibit the largest rotation angle and tilt angle of the oxygen octahedron, the densest microstructure, and the largest grain size among all the samples. The correlation of crystal structure and hybrid improper ferroelectricity confirms that the amplitude of tilt and rotation of oxygen octahedron is crucial to regulate the remnant polarization of Ca3Ti2O7 ceramics. The leakage behaviors, dielectric and ferroelectric properties of Ca3Ti2O7 ceramics are dependent on the microstructure, oxygen vacancy, and grain size caused by different sintering processes, and the related mechanisms have been illuminated. The highest remnant polarization (1.319 μC/cm2) to our knowledge and the lower coercive field (78.17 kV/cm) was achieved in the ceramic sample fabricated by the two-stage sintering, and these findings have an important significance in developing excellent hybrid improper ferroelectric materials.

Combining effects of TiO6 octahedron rotations and random electric fields on structural and properties in Na0.5Bi0.5TiO3

AbstractThe structural and dielectric properties of Na0.5Bi0.5TiO3 (NBT) ceramics and crystals have been investigated and are compared to that of Pb(Zr0.55Ti0.45)O3 (PZT55/45) and Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (PMNT 72/28) ceramics. X‐ray diffraction (XRD) profiles for (100), (110), (111), (200), (220), and (222) (referred to cubic structure) reveal that the monoclinic structure with Cc space group exists both in the NBT single crystal and ceramics. The diffraction profile obtained with high resolution laboratory XRD for the NBT single crystal can be well described, using Cc model instead of R3c model. The dielectric constant of NBT below Thump shows some similarity to that of PZT45/55 ceramics below 50°C in which oxygen octahedron rotations cause the frequency dispersion of the dielectric constant. The temperature‐dependent dielectric constant for NBT can be deconvolved into two independent processes. The lower temperature process shows a typical relaxor characteristic and follows the Vogel‐Fulcher relationship. The other process at higher temperature shows less frequency‐dependent behavior. Comparing the dielectric constant of NBT with that of PZT55/45 and PMNT72/28 reveals that both oxygen octahedral rotations and random electric fields play an important role in the frequency dispersion of the dielectric constant for NBT relaxor feroelectric.

Dual control of magnetism in LaMnO<sub>3</sub>/BaTiO<sub>3</sub> superlattice by epitaxial strain and ferroelectric polarization

The controlling of magnetism of perovskite oxides is scientifically interesting and technically important for numerous functionalities in spintronic devices and next-generation magnetic memories. The experimenally prepared superlattices often contain strain, polarization, oxygen vacancy and other factors, which can affect their magnetic properties. The magnetism of superlattice materials, controlled by using both epitaxial strain and ferroelectric polarization, is not only close to the real state of the material, but also can induce rich physical properties. In this work, we demonstrate a strong magnetoelectric coupling that appears in the LaMnO<sub>3</sub>/ BaTiO<sub>3</sub> superlattice. First-principles calculations reveal that the reversible transitions among ferromagnetism, ferrimagnetism and anti-ferromagnetism are achieved by precisely controlling the magnitude and spin-direction of the magnetic moments of the Mn ions. A maximal change can be achieved to be 100.1% of the net magnetization by switching the ferroelectric polarization, which is much higher than the previous value 93.9%. The half-metallicity is demonstrated in the MnO<sub>2</sub> layer, and accompanied by the spin polarization of the superlattice varying from 100% to 0. In addition, we realize the coexistence of ferroelectric polarization and metallicity, i.e. “ferroelectric metal”. Neither of the strong covalent Mn—O bond and La—O bond acts as an obstacle that prevents the ferroelectric polarization from penetrating the LMO layer. The Jahn-Teller effect, the tilt and rotation of oxygen octahedron, and the charge transfer of the superlattice are systemically analyzed. The variation of strain and re-orientation of polarization lead the electrons to transfer between the e<sub>g</sub> and t<sub>2g</sub> orbitals of Mn, which determines the magnetism of our system. Our purpose-designed LMO/BTO superlattice with robust intrinsic magnetoelectric coupling is a particularly interesting model system that can provide guidance for developing the spintronics for future applications.

Emergence of Topological Hall Effect in a SrRuO3 Single Layer.

Topological Hall effect (THE), appearing as bumps and/or dips in the Hall resistance curves, is considered as a hallmark of the skyrmion spin texture originated from the inversion symmetry breaking and spin-orbit interaction. Recently, Néel-type skyrmion is proposed based on the observed THE in 5d transition metal oxides heterostructures such as SrRuO3 /SrIrO3 bilayers, where the interfacial Dzyaloshinskii-Moriya interaction (DMI), due to the strong spin-orbit coupling (SOC) in SrIrO3 and the broken inversion symmetry at the interface, is believed to play a significant role. Here the emergence of THE in SrRuO3 single layers with thickness ranging from 3 to 6 nm is experimentally demonstrated. It is found that the oxygen octahedron rotation in SrRuO3 also has a significant effect on the observed THE. Furthermore, the THE may be continuously tuned by an applied electrical field. It is proposed that the large SOC of Ru ions together with the broken inversion symmetry, mainly from the interface, produce the DMI that is responsible for the observed THE. The emergence of the gate-tunable DMI in SrRuO3 single layer may stimulate further investigations of new spin-orbit physics in strong SOC oxides.

A New Phase Boundary of Oxygen Octahedral Tilt-Untilt Transition in Bi <sub>0.5</sub>Na <sub>0.5</sub>TiO <sub>3</sub>-PbTiO <sub>3</sub> Piezoelectric Ceramics

The investigation on the fine structure evolutions around morphotropic phase boundary (MPB) is important to understand the origin of high piezoelectricity in ferroelectric ceramics. Here, we discovered a new boundary associated with oxygen octahedron tilt-untilt phase transition by exploring the average and local structure evolutions in the vicinity of the MPB in (Bi0.5Na0.5)TiO3-PbTiO3 (BNT-PT) ceramics. It is found that the local structure transition due to oxygen octahedron rotation is decoupled with the phase transition from rhombohedral to tetragonal phase at MPB in the BNT-PT. Such a local tilt-untilt transition is responsible to the large high-field-induced electrostrain at MPB of the BNT-PT. The crucial difference in MPB between the BNT-PT and the classical piezoelectric Pb(Zr1-xTix)O3 is discussed by linking the structure evolutions to the performance at the MPBs. This work helps us to figure out the origin of the unique large high-field-induced electrostrain in BNT-based ceramics, and may be helpful to the design of high-performance piezoelectric ceramics in the future.

Chemical interpretation, enhanced ferroelectric property and dielectric breakdown strength of CuO-added Sr2Nb2O7 ceramics

The structural interpretation and electrical properties of perovskite layer structured (PLS) Sr2Nb2O7-xwt%CuO ceramics prepared by solid-state reaction method are investigated. The chemical interpretation of enhanced piezoelectricity is confirmed to be attributed to the rotation and/or distortion of oxygen octahedron caused by possible Cu2+ substitution at the A-site of Sr2Nb2O7 by XRD refinement and variable-temperature Raman spectra. Sr2Nb2O7-xwt%CuO (x = 0.3, 0.5 and 0.7) ceramics shows enhanced ferroelectric properties with a larger Pr of ∼4.1 μC/cm2 and a smaller Ec of ∼63.1 kV/cm. This study further explains the cations in A-site play a major structural role in the polarization process for PLS system. It was found that dielectric breakdown strength increases up to 258.8 kV/cm and then decreases gradually with the increase of CuO content. Impedance spectroscopy indicated that CuO addition could be helpful in increasing the grain boundary resistance then dielectric breakdown strength.

Low‐temperature sintering and electrical properties of Sr2Nb2O7 piezoceramics by CuO addition

AbstractEffects of 0.5 wt% CuO addition on the sintering, structural and electrical properties of perovskite layer structured (PLS) Sr2Nb2O7 ceramics prepared by solid‐state reaction method are investigated. The addition of CuO is beneficial to the liquid phase bridge formation at sintering process, leading to lower sintering temperature of 1180°C and larger bulk density up to 98%. Meanwhile, CuO modified Sr2Nb2O7 ceramics show a remarkable d33 of (1.1 ± 0.1) pC/N while still with a very high Tc of (1340 ± 2)°C. Raman spectra indicate that the improvement of piezoelectricity could be attributed to the rotation and/or distortion of oxygen octahedron caused by possible Cu2+ substitution at the A‐sites of Sr2Nb2O7.

Structure and electrical properties of perovskite layer (1−x)Sr2Nb2O7‐x(Na0.5Bi0.5)TiO3 high‐temperature piezoceramics

AbstractThe structure and electrical properties of perovskite layer structured (PLS) (1−x)Sr2Nb2O7‐x(Na0.5Bi0.5)TiO3 (SNO‐NBT) prepared by solid‐state reaction method are investigated. The addition of NBT is beneficial to speed up mass transfer and particle rearrangement during sintering, leading to better sinterability and higher bulk density up to 96.8%. The solid solution limit x in the SNO‐NBT system is below 0.03, over which Ti4+ is preferable to aggregate and results in the generation of secondary phase. After the modification by NBT, all SNO‐NBT ceramics have a Curie temperature Tc up to over 1300°C and piezoelectric constant d33 about 1.0 pC/N. The breakthrough of piezoelectricity can mainly be attributed to rotation and distortion of oxygen octahedron as well as higher poling electric field resulting from the improved bulk density. This study not only demonstrates how to improve piezoelectricity by NBT addition, but also opens up a new direction to design PLS piezoceramics by introducing appropriate second phase.

Atomic-level study ofBiFeO3under epitaxial strain

Structural and thermal properties of $\mathrm{BiFe}{\mathrm{O}}_{3}$ under compressive epitaxial strain are investigated using a shell model fitted to first-principles calculations. We show that a model developed for the bulk describes properly the behavior of the compound as function of the strain, including the appearance of tetragonallike phase with a large $c/a$ ratio. The obtained temperature-strain phase diagram reproduces several features observed experimentally in thin films. Molecular dynamic simulations show that morphotropic phase boundary separating the $R$-like and $T$-like regions is temperature independent but with different phases along the transition region. The microscopic analysis of the temperature-strain phase diagram emphasizes the relevance of the interplay between polarization, oxygen octahedron rotations, and strain.

Stabilization of Highly PolarBiFeO3-like Structure: A New Interface Design Route for Enhanced Ferroelectricity in Artificial Perovskite Superlattices

In ABO3 perovskites, oxygen octahedron rotations are common structural distortions that can promote large ferroelectricity in BiFeO3 with an R3c structure [1], but suppress ferroelectricity in CaTiO3 with a Pbnm symmetry [2]. For many CaTiO3-like perovskites, the BiFeO3 structure is a metastable phase. Here, we report the stabilization of the highly-polar BiFeO3-like phase of CaTiO3 in a BaTiO3/CaTiO3 superlattice grown on a SrTiO3 substrate. The stabilization is realized by a reconstruction of oxygen octahedron rotations at the interface from the pattern of nonpolar bulk CaTiO3 to a different pattern that is characteristic of a BiFeO3 phase. The reconstruction is interpreted through a combination of amplitude-contrast sub 0.1nm high-resolution transmission electron microscopy and first-principles theories of the structure, energetics, and polarization of the superlattice and its constituents. We further predict a number of new artificial ferroelectric materials demonstrating that nonpolar perovskites can be turned into ferroelectrics via this interface mechanism. Therefore, a large number of perovskites with the CaTiO3 structure type, which include many magnetic representatives, are now good candidates as novel highly-polar multiferroic materials [3].

B11-O-11Atomic-scale Tracking Cation Diffusion in Lithium Manganese Oxide

Solid-state phase transition are ubiquitous and of critical importance to numerous technological applications, including energy conversion and storage systems. These transition processes involve local atomic displacements or long-range atom migration without adding/reducing any atoms. For example, in perovskite ferroelectrics the oxygen octahedron shift and/or rotation results in a first order phase transition-polarization switching [ 1 ]. Investigating the dynamic processes of phase transformation in solids is critical to gain insights to understanding the fundamental physical properties of functional materials and benefiting industrial technologies. Here, we track full atoms motion/shift in lithium manganese oxide during a phase transition from spinel to rocksalt by using atomically resolved aberration corrected scanning transmission electron microscopy and spectroscopy. We find that given energy the transition metal cations can readily hop between oxygen tetrahedral and octahedral sites in lithium manganese oxide similar to lithium diffusion behavior, leaving the anion structure framework almost unchanged. During phase transition, the transition metal cation migration path, intermediate state, migration length, and atomic structure of phase boundaries are discovered and the mechanism is discussed. Our observations help us to understand the past experimental phenomena and provide useful information to stabilize the structure of electrode materials and thus improve the life of lithium ion batteries.

Phase transitions and antiferroelectricity inBiFeO3from atomic-level simulations

The structural and polar properties of $\mathrm{BiFe}{\mathrm{O}}_{3}$ at finite temperature are investigated using an atomistic shell model fitted to first-principles calculations. Molecular dynamics simulations show a direct transition from the low-temperature $R3c$ ferroelectric phase to the Pbnm orthorhombic phase without evidence of any intermediate bridging phase between them. The high-temperature phase is characterized by the presence of two sublattices with opposite polarizations, and it displays the characteristic double-hysteresis loop under the action of an external electric field. The microscopic analysis reveals that the change in the polar direction and the large lattice strains observed during the antiferroelectric-ferroelectric phase transition originate from the interplay between polarization, oxygen octahedron rotations, and strain. As a result, the induced ferroelectric phase recovers the symmetry of the low-temperature $R3c$ phase.

Large in-plane deformation of RuO6octahedron and ferromagnetism of bulk SrRuO3

Glazer tilting system with tilting and rotation of oxygen octahedron, can describe ABO3 perovskite structure effectively. In highest symmetry, Pm-3m(No. 221) crystal structure is a0a0a0 without tilting and rotation. If temperature is lower, the different atomic radius of A and B causes tilting and rotation of BO6 octahedron. Glazer tiling notation of Pbnm(No. 62, cab lattice) orthorhombic structure is a-a-c+ with antiphase tilting along [110]cubic and in-phase rotation along [001]cubic for neighboring octahedron. SrRuO3 is rare example of itinerant ferromagnetic among 4d oxides. It shows zero thermal expansion, so called Invar effect below ferromagnetic transition(Tc=165 K). Otherwise, paramagnetic CaRuO3 has same Pbnm crystal structure without magnetic transition. To understand Invar effect and ferromagnetism of SrRuO3, We carried out high resolution Time-of-flight powder neutron diffraction using SuperHRPD beamline in J-PARC, with the best resolution Δd/d=0.03% of backscattering bank. Itinerant ferromagnetic SrRuO3 shows 50 fetometer increase of <Ru-O> mean bond below ferromagnetic transition while paramagnetic CaRuO3 shows decrease of <Ru-O> and follows well by the usual thermal expansion. For SrRuO3, Glazer tilting with deformation of RuO6 octahedron explains Invar effect and why lattice a is larger than lattice b in Pbnm structure. The increased <Ru-O> mean bond is considered as coupled order parameter with ferromagnetic transition. The band width of CaRuO3 is almost constant in the whole temperature range whereas ones of SrRuO3 decrease at low temperature. Then more localized Ru 4d orbitals probably contribute ferromagnetic transition.

Polarization enhancement in perovskite superlattices by oxygen octahedral tilts

Interface engineering in perovskite oxide superlattices has developed into a flourishing field, enabling not only further tuning of the exceptional properties, but also giving access to emergent physical phenomena. Here, we reveal a new mechanism for enhancing the electric polarization by the interface-induced oxygen octahedral tilts in BaTiO3/CaTiO3 superlattices. By combining a novel genetic algorithm with density functional theory (DFT), we predict that the true ground states in 1:1 and 2:2 BaTiO3/CaTiO3 superlattices grown on SrTiO3 adopt Pc symmetry with a large proper electric polarization (32.8μC/cm2 for 1:1 and 35.8μC/cm2 for 2:2 superlattices), which is even larger than that of bulk BaTiO3. The tilt of oxygen octahedron is found to play a key role for the enhancement of out-of-plane polarization in 1:1 superlattices because it reduces greatly the rotation of oxygen octahedron (out-of-phase) which significantly suppresses the out-of-plane polarization.

Strong coupling of Jahn-Teller distortion to oxygen-octahedron rotation and functional properties in epitaxially strained orthorhombic LaMnO3

First-principles calculations reveal a large cooperative coupling of Jahn-Teller (JT) distortion to oxygen-octahedron rotations in perovskite LaMnO$_3$. The combination of the two distortions is responsible for stabilizing the strongly orthorhombic $A$-AFM insulating ($I$) $Pbnm$ ground state relative to a metallic ferromagnetic (FM-$M$) phase. However, epitaxial strain due to coherent matching to a crystalline substrate can change the relative stability of the two states. In particular, coherent matching to a square-lattice substrate favors the less orthorhombic FM-$M$ phase, with the $A$-AFM phase stabilized at higher values of tensile epitaxial strain due to its larger volume per formula unit, resulting in a coupled magnetic and metal-insulator transition at a critical strain close to 1%. At the phase boundary, colossal magneto-resistance is expected. Tensile epitaxial strain enhances the JT distortion and opens the band gap in the $A$-AFM-$I$ $c$-$Pbnm$ phase, offering the opportunity for band-gap engineering. Compressive epitaxial strain induces an orientational transition within the FM-$M$ phase from $c$-$Pbnm$ to $ab$-$Pbnm$ with a change in the direction of the magnetic easy axis relative to the substrate, yielding strain-controlled magnetization at the phase boundary. The strong couplings between the JT distortion, the oxygen-octahedron rotations and the magnetic and electronic properties, and associated functional behavior, motivate interest in other orthorhombic $Pbnm$ perovskites with large JT distortions, which should also exhibit a rich variety of coupled magnetic, structural and electronic phase transitions driven by epitaxial strain.

Low-symmetry monoclinic ferroelectric phase stabilized by oxygen octahedra rotations in strained EuxSr1−xTiO3thin films

Using Landau--Ginzburg--Devonshire theory and phase-field modeling, we explore the complex interplay between a structural order parameter (oxygen octahedron rotation) and polarization in Eu${}_{x}$Sr${}_{1\ensuremath{-}x}$TiO${}_{3}$ thin films. Under a biaxially tensile strain, a low-symmetry monoclinic phase with in-plane ferroelectric polarization is found to be stabilized by antiferrodistortive oxygen octahedra tilts. The monoclinic phase is stable over a wide temperature range. It is characterized by a large number of energetically equivalent polar and structural twin domains. This work demonstrates the development of a spontaneous polarization and piezo- and pyroelectricity in a ferroelastic twin boundary arising from flexoelectric coupling and rotostriction.

New multiferroics based on EuxSr1−xTiO3 nanotubes and nanowires

Using Landau-Ginzburg-Devonshire theory, we have addressed the complex interplay between structural antiferrodistortive order parameter (oxygen octahedron rotations), polarization and magnetization in EuxSr1−xTiO3 nanosystems. We have calculated the phase diagrams of EuxSr1−xTiO3 bulk, nanotubes and nanowires, which include the antiferrodistortive, ferroelectric, ferromagnetic, and antiferromagnetic phases. For EuxSr1−xTiO3 nanosystems, our calculations show the presence of antiferrodistortive-ferroelectric-ferromagnetic phase or the triple phase at low temperatures (≤10 K). The polarization and magnetization values in the triple phase are calculated to be relatively high (∼50 μC/cm2 and ∼0.5 MA/m). Therefore, the strong coupling between structural distortions, polarization, and magnetization suggests the EuxSr1−xTiO3 nanosystems as strong candidates for possible multiferroic applications.