Search

Piezoelectric ceramics exhibit three conventional piezoelectric coefficients, i.e., d33, d31, d15, due to their ∞ m m crystal symmetry. Unconventional piezoelectric coefficients, such as d11, d12, d13, d14, d16, etc., can only be extracted from piezoelectric single crystals of special symmetry with specific cut direction. Here we demonstrate a rotated poling method to realize unconventional piezoelectric coefficients in perovskite piezoelectric ceramics. This method is elaborated in theory and experimentally proven to be effective. Full nonzero piezoelectric coefficients in the 3 × 6 piezoelectric coefficients matrix can be obtained by combining these “quasi (effective) piezoelectric coefficients” with the conventional piezoelectric coefficients, which would expand applications in a wide variety of piezoelectric devices.

Strain-mediated magnetoelectric effect can be utilized as an energy-efficient approach for spin manipulation. However, over 90° magnetization rotation is still challenging in un-patterned magnetic films, as the piezo-strain driven by ferroelectric domain switching is generally uniaxial rather than unidirectional, which limits the developments of non-volatile magnetic memory and logic devices. Here we demonstrate the rotation of local magnetization with a large angle of 136° by applying strains with a shear component at a fixed magnetic field of 45 Oe in FeCoSiB/PMN-PT (011) multiferroic heterostructures, revealed by a vector-resolved quantitative magneto-optical Kerr effect (MOKE) microscopy. Phase-field simulations confirm that the approximate 140° rotation of magnetization vectors is a consequence of the shear strain associated with ferroelectric/ferroelastic switching of PMN-PT (011) substrates. The visualization of over 90° magnetization rotation induced by the strain with a shear component paves the way for deterministic magnetization switching that has important implications in the energy-efficient spintronic devices.

Voltage control magnetism is one of the most energy efficient pathway towards magnetoelectric (ME) device. Ionic liquid gating (ILG) method has already shown impressive manipulation power at the IL/electrode interface to influence the structure, orbital as well as spin of the electrode materials. As key material in anisotropy magnetoresistance sensor and spin valve heterostructure, the permalloy Ni0.81Fe0.19 was utilized as the electrode to investigate the ILG induced magnetic anisotropy change. In this work, we realized magnetic anisotropy control in Au/[DEME]+[TFSI]-/Ni0.81Fe0.19 (2.5 nm)/Ta heterostructure via ILG caused electrostatic doping. This is evidenced in situ reversible ferromagnetic field (Hr) shift with electron spin resonance (ESR) spectrometer. Aiming at the question whether the charge accumulation at the ionic liquid interface is the main control mechanism at low voltage, we carefully tested the relationship between the change of resonance field and the amount of surface charge. It was found that these two had a good linear relationship between −1 V and +1 V. Defining the linear parameter as A whose value is 28.7 mT m2/Col. Unlike previously reported chemical regulation of Co, this article used ionic liquids to physically regulate NiFe, which has not been studied in the previous ionic liquid regulation. And NiFe has a narrower resonance line width for easy reference to microwave devices. In addition, It also has a stronger ferromagnetic signal than Co, which can be more easily detected as a sensor device. Therefore, this system is more promising. The ILG control NiFe may lead to a new kind of magnetoelectric sensor devices and path a new way to low energy consumption spintronics.

Piezoelectric devices based on d36 mode are remarkably stable that depolarization rarely occurs in d36 face shear mode, because d36 mode is completely different from d15 thickness shear mode, where the applied electric field is perpendicular to poling direction and depolarization is ineluctable due to 90° dipole rotation. However, piezoelectric ceramics conventionally possess three piezoelectric coefficients (i.e., d33, d31, and d15), while d36 only exists in single crystals of specific point groups and cut directions. In this work, we propose a method to realize d36 piezoelectric coefficient in tetragonal piezoelectric ceramics by mechanical and electric domain engineering. This method is successfully applied in bismuth scandium-lead titanate (abbreviated as BS-PT) high-temperature piezoelectric ceramics with a resultant d36 up to 160 pC/N, which broadens the application of BS-PT ceramics, such as face shear actuator, energy harvester, transducer, etc. We find that domain engineering by transversal electric poling is preferred compared with the transversal mechanical poling, due to the simpler process, higher reliability, and higher resultant d36 piezoelectric coefficient. By combining the Diffraction-Plane-Transformation (DPT) model with the domain engineering via transversal electric poling, we demonstrate a quantitative domain engineering method for the first time, which could be used for optimizing the piezoelectric properties by precise design of the domain structures in piezoelectric materials.

Ferroelectric resistive switching has recently attracted considerable attention as a promising candidate for next-generation non-volatile memory. In this work, we report an electro and photon double-driven bipolar resistive switching behavior in Pt /Bi0.9Eu0.1FeO3 (BEFO) /Nb-doped SrTiO3 (NSTO) heterostructures prepared via pulsed laser deposition. In addition to the polarization-based control of the resistive memory, a switchable photovoltaic effect is observed that can be used to detect the polarization direction non-destructively. Significantly, the electric field-modulated interfacial barrier can be further affected by photon-generated carriers. This phenomenon is attributed to the barrier modulation in the Pt /BEFO and BEFO /NSTO interfaces by electric field and photon excitation. These results indicate the feasibility of non-volatile and non-destructive readout from ferroelectric memory.

Uranium is well-known to have serious adverse effects on the ecological environment and human health. Bioremediation stands out among many remediation methods owing to its being economically feasible and environmentally friendly. This study reported a great promising strategy for eliminating uranium by Stenotrophomonas sp. CICC 23833 in the aquatic environment. The bacterium demonstrated excellent uranium adsorption capacity (q

Multiferroic Bi(1+x)×0.85Nd0.15FeO3 (BNF) ceramics with various Bi contents are prepared by conventional solid state reaction, and the effects of excess Bi on the structure, morphology, dielectric, ferroelectric, and magnetic properties are investigated. XRD patterns show the coexistence of rhombohedral and orthorhombic phase in all BNF ceramics due to the doping of Nd3+ ions. Bi2Fe4O9 and Bi2O3 impurity can be observed in x = 0 and x = 5%, 7.5% ceramics, respectively. Surface morphologies are closely related to the Bi content and x = 2.5% sample exhibits the largest average grain size of ∼6.72 μm. The leakage current density has been decreased by 3–4 orders of magnitudes through excess Bi. The x = 2.5% sample shows good ferroelectric property with typical hysteresis loop and a large remnant polarization of about 42 μC/cm2 at 150 kV/cm. The P-E hysteresis deteriorates in x = 5% and x = 7.5% ceramics. The PbZrO3-like superstructure related to 1/4(hh0)p diffraction spots in SAED pattern can be found in all BNF ceramics and the number of grain with superstructure observed in each sample decreases as the Bi content increases. As Bi content increases, the remnant magnetization decreases at first, and then increases. Conversion-electron Mossbauer study have ruled out the impacts of Fe2+, Fe4+, or γ-Fe2O3 on the magnetic properties, suggesting that the weak ferromagnetism comes from the destroy of spin cycloid through substitution of Bi3+ ions with Nd3+ ions. Excessive Bi3+ ions have weakened the effect of Nd3+ ions on suppression of spin cycloid and resulted in the degradation of magnetic properties. The slight improvement of magnetic properties in x = 7.5% sample is considered to attribute to Fe vacancies induced by excessive Bi.

The magnetoelectric (ME) materials and related devices have been attracting increasing research attention over the last few years. They exhibit strong ME coupling effect at room temperature, and electric field control of magnetization or magnetic field control of ferroelectric polarization can be achieved. The ME coupling effect brings novel functionalities to develop ultra-fast, low-power, and miniaturized electronics. Recent progress shows the performance of ME materials is further improved and the materials are used to develop many new types of electronics such as high-speed memory, radio frequency resonator, compact ME antenna, and weak magnetic field sensor. In this review, we present the overview in those fields with emphasis on both the opportunities and challenges for the application of ME materials and devices in the cutting-edge technologies.

The flexible La0.7Sr0.3MnO3 (LSMO) film shows good mechanical stretchability and property stability under bending states, which makes it a candidate material for flexible electronics and spintronics devices. Here the microwave magnetism of flexible LSMO thin film has been manipulated effectively by the ionic gel (IG) gating process. A reversible and non-volatile magnetoelectric (ME) coefficient of 50 Oe/V was observed using electron paramagnetic resonance (ESR) technology at the flat multilayer structure. This ME coupling is caused by the electrons hopping between Mn3+ and Mn4+ ions under the interfacial electric double layer. When the membranes were bent to a radius of curvature of 15 mm, a larger ME coefficient of 67 Oe/V was also observed, which indicating that this flexible structure can work effectively under mechanical deformation. This work demonstrates the voltage control of magnetism for flexible correlated materials and paves a way towards wearable low-power devices based on flexible manganite films.

Multilayer Pt/BaTiO 3 /BiFeO 3 /TiO 2 heterostructure was fabricated on FTO substrates by sol-gel technique. This heterostructure shows strong light absorption, sensitive optical switching response, and excellent photovoltaic properties, which are effectively modulated by the ferroelectric polarization. The short circuit current density and open circuit voltage of the multilayer heterostructure are significantly enhanced compared with that of the single layer BiFeO 3 thin film under the initial and positive polarization states. Analysis on the schematic energy band diagrams suggests that the excellent photovoltaic properties can be attributed to the interface Schottky barrier regulated by ferroelectric polarization, in which the TiO 2 layer acts as the electron collection layer, and the ferroelectric BaTiO 3 layer acts as a hole collection layer and also an auxiliary photovoltaic absorption layer to enhance optical absorption properties, thus improve the light absorption efficiency and the separation of electron-hole pairs. These results provide a promising method to optimize the performance of ferroelectric photovoltaic devices by using multilayer heterostructure.

In this paper, we demonstrate a nonvolatile modulation effect on the magnetic properties by electric (E)-field-induced ferroelectric (FE) polarizing in Bi0.95Ba0.05FeO3 single-phase multiferroics. It is found that E-field has much effect on weak ferromagnetic order, but has little effect on strong antiferromagnetic order in the sample. The change of Raman scattering spectra with different FE polar states of the sample, as well as the magnetization change under different polarization times (tp), indicates that the modulation effect on magnetism comes from E-field-induced the change of FE polarization, which couples with magnetic moments in Bi0.95Ba0.05FeO3 sample.

We report the growth of ferroelectric Pb 0.92 La 0.08 Zr 0.52 Ti 0.48 O 3 (PLZT) thick films using a poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA)-modified sol–gel process. A per-coating thickness of ≈0.66 μm has been demonstrated using PVP/VA-modified solution, which is more than doubled that of the PLZT films grown by PVP-modified method, and nearly 6 times the per-coating thickness of films prepared by conventional sol–gel process. PLZT thick films grown on LNO/Ni substrates exhibited denser microstructure, higher remanent polarization (11 μC/cm 2 ) and dielectric tunability (45%), lower leakage current density (≈1.2 × 10 −8 A/cm 2 ), and higher breakdown strength (≈1.6 MV/cm) than those for the samples grown on PtSi substrates. These results demonstrated great potential of using PVP/VA-modified sol–gel process for high power film capacitor applications.

In situ tuning effect on magnetism is often achieved by electric-field-induced inverse piezoelectric effect in ferromagnetic/piezoelectric structures. Here, we report on a non-volatile tuning of magnetic properties in Ni/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure. Both magnetization difference of up to 60% and coercivity difference of up to 23.2% are obtained by electric-field-induced the change of polar state in the substrate. This modulation effect is observed over a broad range of temperatures. The coincident changes of both magnetic properties and Raman scattering spectra with different polarization times for the heterostructure are detected, which indicates that the non-volatile tuning effect on magnetism is attributed to the change of the magnetic anisotropy result from the ferroelectric polarizing induced-strain.

High power microwave devices have been suffering from secondary electron yield (SEY), which occurs at the surface and leads to increases in energy dissipate and noise level in microwave cavities. The suppression of SEY in microwave materials is significant for space applications. In this work, we report a surface roughness evolution mechanism induced by carbon coating on a widely-used microwave cavity material Ag/Al. The competition between the preferred growth and the island growth modes leads to the roughness enhancement in the 60 nm carbon coated Ag/Al substrates. By extracting the smooth factor Ks in Vaughan model from the angular dependent SEY measurement, we attribute the suppression of SEY to the intrinsic low SEY of the carbon film and the high surface roughness. Our work demonstrates a low-cost, easy-to-scale coating process to effectively prevent the formation of secondary electron avalanche in space borne microwave devices.

We incorporated a ≈5-nm-thick MnO x insertion layer in the middle of a ≈1.38-μm-thick Pb 0.92 La 0.08 Zr 0.52 Ti 0.48 O 3 (PLZT) film grown by a modified sol–gel process and measured the dielectric and ferroelectric properties of PLZT films with and without MnO x insertion layer. By incorporation of the MnO x layer, residual stress was reduced from ≈350 MPa to ≈125 MPa, dielectric permittivity decreased from ≈1300 to ≈950, while dielectric loss increased from ≈0.04 to ≈0.07 as measured at 10 kHz. Also, remanent polarization increased from ≈9.1 μC/cm 2 to ≈11.7 μC/cm 2 , coercive field increased from ≈28.7 kV/cm to ≈40.3 kV/cm, and internal bias field from ≈3 kV/cm to ≈14 kV/cm. We have observed decreased irreversible Rayleigh coefficient and dielectric nonlinearity on samples with MnO x insertion layer. These changes in properties are attributable to Mn cation doping as acceptors near the MnO x /PLZT interface, which forms oxygen vacancies and defect induced dipoles like 2 M n ′ T i − V O • • (or M n ″ T i − V O • • ), acting effectively as pinning centers to hinder domain wall movement.

The microstructures of Bi 0.85 Nd 0.15 FeO 3 ceramics were investigated by using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), convergent-beam electron diffraction (CBED) and X-ray energy dispersive spectrometry (EDS). The superstructure phase related to 1/4( hh 0) p and 1/4(00 l ) p diffraction spots were observed in the samples. It is found that the superstructure phase can co-exist with R 3 c phase in a single grain. The bright and dark field images accompanied with SAED patterns provided evidences of the superstructure phase dispersed into the matrix with R3c symmetry and evolution of the domain. The ferroelectric domain wall was observed according to the displacement of Fe 3+ ions respect to Bi 3+ sub-lattice in the ferroelectric R 3 c phase based on HRTEM observations. The space group Pnam of the superstructure was identified by combining SAED and CBED techniques. EDS measurement revealed that the concentration of Nd in the Pnam phase is higher than that in R 3 c phase. This might mean that the transition from R 3 c to Pnam structure is due to the inhomogeneous distribution of the Nd concentration and the weakened stereochemical activity of Bi 3+ lone electron pair, arisen from the increase in Nd content.

The yittra-stablized zirconia (YSZ) thin film was deposited on a Nb:SrTiO 3 (NSTO) substrate by pulsed laser deposition to form a Pt/YSZ/NSTO heterostructure device. This device exhibits high resistive switching ratio of 10 5 at a read voltage of −0.1 V after applied +3 V/−4 V pulse voltages. Moreover, the resistance states could be reversibly switched among multilevel resistance states by changing the magnitude of Set or Reset pulse voltages, which shows potential application in multilevel nonvolatile memory devices. The RS mechanism of the device could be attributed to the modulation of YSZ/NSTO Schottky-like junction depletion, which is caused by the carrier injection-trapped/detrapped process under the applied electric field.

Integration of oxides onto base metal substrates offers great advantages in cost and weight reduction, device miniaturization, and flexibility in packaging. In this work, we report the deposition of dielectric Pb0.92La0.08Zr0.52Ti0.48O3−δ (PLZT 8/52/48) films on aluminum foils by an in-air crystallization process. Film-on-foil structures with and without conductive oxide LaNiO3 (LNO) buffer layer between PLZT film and aluminum foil were tested. Utilization of LNO buffer layer dramatically improved the dielectric and ferroelectric properties of the overlying PLZT compared with those for films deposited directly on aluminum. The improvements in electrical properties were attributed to the suppression of cubic non-ferroelectric layer at the metal/dielectric interface by LNO buffer layer. This work can be extended to the integration of other functional oxide materials with light, conductive, and inexpensive aluminum substrates for a broad range of applications.

A magneto-mechano-electric (MME) device for energy harvesting from ambient low-frequency magnetic field is investigated in this study. Consisting of piezoelectric ceramic rings, NdFeB permanent magnets and union piece, the proposed MME energy harvester is designed with the barbell-shaped structure operating in d33 mode. NdFeB permanent magnets are attached at the free end of barbell-shaped structure, which can produce compressive stress on the piezoelectric ceramic rings via magnetic torque effect. The properties of the MME energy harvester are optimized by using the finite element analysis. Two electrode shapes, including full electrode and divided electrode, are investigated in the aspect of their influences on the device performance. The finite element analysis is consistent with the experimental results, revealing that the electrode shape of piezoelectric ceramic rings is crucial for the performance of the proposed MME device. The MME device presents a low resonant frequency ( 10 V @ 10 Oe), a maximum output power of ˜10.5 μW and a maximum power density of 3.5 μW/Oe cm3, demonstrating the potential applications for harvesting ambient low-frequency magnetic field energy.

Fe3O4 nanopillars with remarkably high uniformity and crystallinity are grown on (100)-oriented magnesium aluminate substrates by pulsed laser deposition with a simple anodic-aluminum-oxide template method. Compared with Fe3O4 full film, the nanopillars exhibit higher in-plane magnetic saturation field and lower out-of-plane saturation field. The angular-dependent ferromagnetic resonance, investigated by electron spin resonance spectroscopy, confirms the shape-induced anisotropy change in Fe3O4 nanopillars. High Gilbert damping parameter of 0.23 is obtained by measuring the resonance field at different microwave frequencies.

A series of TiO 2 photoanodes with differing amounts of Ag nanoparticles (NPs) on TiO 2 in core-shell form (Ag@TiO 2 ) are prepared and used to make a series of dye-sensitized solar cells (DSSCs). The influence of different amounts of Ag–NPs on the structure and performance of the DSSCs is investigated. Studies indicate that the short-circuit current density (J sc ), open-circuit voltage (V oc ), charge lifetime and dark current of DSSCs containing Ag–NPs are significantly improved. The best performance is achieved in the DSSCs with 0.15 wt% Ag–NPs additions, with the maximum J sc of 10.19 mA cm −2 , highest V oc of 698 mV and best photoelectric conversion efficiency of 5.33%, significantly superior to that of the DSSCs with pure TiO 2 photoanodes. The increase of J sc is attributed to the enhanced dye light absorption in strength and spectral range due to the surface plasmon resonance of Ag–NPs in photoanode, while the increase of V oc may be related to the more negative level of the quasi-Fermi energy of Ag–TiO 2 composite system resulting from the added Ag.

This paper reports the bipolar resistive switching effect in a SrTiO"3/NiO stacked heterostructure which was epitaxially deposited on an Nb doped SrTiO"3 substrate by pulsed laser deposition. This heterostructure shows high resistive switching ratio of over 10^4 at the read voltage of -0.5V and an expected retention ability of ten years, which is better than that of NiO-based device. Moreover, the resistive switching ratio can be adjusted by changing the maximum applied voltage or compliance current, which shows promising for multilevel nonvolatile memories application. Meanwhile, these results have been discussed by carrier injection-trapped/detrapped process.

The CoFe2O4 (CFO)/Bi3.15Nd0.85Ti3O12 (BNT) multiferroic composite coaxial nanotubes were prepared by a sol–gel template method. The morphologies of the coaxial nanotubes were characterized and the selected area electron diffraction patterns confirmed the coexistence of spinel CFO and perovskite BNT phase. The vibrating sample magnetometer measurements showed that the saturation magnetization and coercive field of the coaxial nanotubes were 1 emu/g and 0.7 kOe, respectively, which was contributed totally from the inner CFO nanotubes. The CFO/BNT coaxial nanotubes showed typical ferroelectric hysteresis loop, while the increased leakage current density is likely due to the high conductivity in the inner CFO nanotubes. Our study demonstrated that the CFO/BNT coaxial nanotubes were of both ferroelectric and magnetic features in nanoscale.

A series of dye-sensitized solar cells (DSSCs) with different graphene-P25 (G-P25) photoelectrodes were prepared by a ball milling method. The influences of graphene on the structures and performance of G-P25 cells were studied. Studies indicated that the rutile contents in G-P25 photoelectrodes increased with increasing graphene-oxide (GO) additions and reached the maximum value at GO addition of 4.5 ml. And with the increase of GO additions, the porosity of the G-P25 photoelectrodes, the interface recombination resistances, and the short current densities increased. When the GO addition was 4.5 ml, the G-P25 cells showed the best performance with the largest interface recombination resistance of 15.12 Ω and the largest photoelectric conversion efficiency of 5.09%, which was remarkably higher than those of pure P25 DSSC. Since the tendency of the photoelectric conversion efficiency varying with the GO additions was in consistence with that of the rutile contents, the enhancement of the photoelectric conversion properties of the G-P25 DSSCs was preliminary attributed to the increase of the rutile contents and the porosity in the photoelectrodes due to graphene adding.

Pure BiFeO3 (BFO), 15% Nd doped BFO (BNF), and 15% Nd and 2% high-valence Mn co-doped BFO (BNFM) multiferroic ceramics were prepared by a rapid liquid phase sintering technique. A structural transition from rhombohedral R 3 c to orthorhombic P 4 m m occurred in the BNF and BNFM ceramics. The co-doped BNFM ceramics exhibit the largest dielectric constant, the smallest dielectric loss and leakage current, and an improved rectangular-shaped polarization hysteresis loop with a remnant polarization as high as 31 μC/cm2, which could be attributed to the lower concentration of charge defects and the structural transition. Besides, enhanced ferromagnetism is confirmed in BNFM with a remnant magnetization of 0.075 emu/g and a coercive magnetic field of 5.8 kOe, which might be attributed to the effective suppression of the spatially modulated spin structure by the Nd and Mn co-doping.

Ba-doped BiFeO 3 thin films were prepared on Pt/TiO 2 /SiO 2 /Si (100) substrate at various oxygen pressures by pulsed laser deposition. The influences of oxygen pressure on the crystalline structures, magnetic and electrical properties of these films were studied. Studies showed that the oxygen vacancy content and accordingly the leakage current density of the films decreased with the increase of the oxygen pressure, and the concentration of the Fe 2+ increased with the decrease of the oxygen pressure. Strong ferromagnetism was observed in these films. The magnetization of the films increased with the decrease of the oxygen pressure and the largest remnant magnetization of 2.46 × 10 4 A/m was obtained at an oxygen pressure of 0.7 Pa. This enhancement of the magnetization can be attributed to the increase of the Fe 2+ concentration which may be related closely to the increase of the oxygen vacancy in the films.

The pressure effect on the magnetic and crystallographic structures of the materials UCu 2 Ge 2 , and U(Ni 0.05 Cu 0.95 ) 2 Ge 2 are studied by neutron diffraction in the applied pressure range of ambient to 0.63 GPa, at room temperature and 60 K. The compressibilities of the materials are found to be isotropic, and very similar for both materials and temperatures. This isotropy is explained by a free-electron gas control of the compressibility. No pressure effect on the magnetic structures or on the magnitude of the magnetic moments was observed for both materials. This result is discussed in the framework of the RKKY model.

In situ neutron powder diffraction has been used to show that the application of hydrostatic pressure at room temperature produces a transformation of ZrW 2 O 8 from the cubic to an orthorhombic phase beginning at 2.1 kbar and completed by 3.1 kbar, with a 5% reduction in volume. After release of pressure, the orthorhombic phase is retained at room temperature. Its thermal expansion is negative below room temperature, but is positive above room temperature with a transformation back to the cubic phase at about 390 K. The WO 4 groups are found to play the dominant role in both phase transformations. The volume compressibilities of the cubic and orthorhombic phases are 1.38 × 10 −3 and 1.53 × 10 −3 kbar −1 , respectively.

The structures of R2Fe17−xAlxC1 (R = Y, Pr, Tb, Ho, Er; x = 2, 4) have been studied with neutron diffraction. All of the compounds have the rhombohedral Th2Zn17 structure (space group R-3m) except for the Er series which has the disordered hexagonal Th2Ni17 structure (space group P 63/mmc). Both substitution of Fe and interstitial C can trigger the structure change from hexagonal to rhombohedral in the heavy rare-earth 2 : 17 compounds. In the rhombohedral compounds, Al is found to prefer the 18th site and fills up the 6c site more rapidly at higher Al concentration. No Al is found at the 9d site. C is mainly found at the 9e site. In the Pr compounds, a small amount of C is also found at the 18g site. In the Er samples, al is found at the Fe 6g site which is the equivalent of the 9d site in the rhombohedral structure.