Distortion Of Oxygen Octahedra Research Articles

Effects of heterovalent ions doping-induced oxygen octahedral distortion and defect chemical change on piezoelectric characteristics and thermal stability of PHT-PIN ceramics

Electromechanical devices require functional materials possessing excellent piezoelectric properties, good thermal stability, and high electromechanical coupling coefficients. To modulate the piezoelectric, dielectric, and electromechanical characteristics of 0.89Pb(Hf0.47Ti0.53)O3-0.11Pb(In1/2Nb1/2)O3 (PHT-PIN) piezoelectric ceramics, heterovalent ions of lithium (Li) and tungsten (W) were doped through a traditional solid-phase reaction approach. On the one hand, large lattice distortions caused by the doped W6+ resulted in the shortening of BO bonds while an increase in the local displacement of B-site ions. Moreover, a mismatch occurred for the oxygen octahedral dimensions, and a subsequent disruption of the long-ranged ordered ferroelectric domains was observed, which resulted in the formation of microdomains. On the other hand, the changes in the concentration of oxygen vacancy defects induced by the Li and W doping inside the ceramic were comprehensively analyzed. The decrease in the concentration of oxygen vacancies was found to be accompanied by the enhancement of piezoelectric properties of the material. Excellent comprehensive performance (piezoelectric coefficient d33 = 655 pC N−1, Curie temperature Tc = 321.1 °C, dielectric constantεr = 3352.31, electromechanical coupling coefficient kp = 0.67, and residual polarization strength Pr = 55 μC cm−2) was obtained for 0.2 mol % doping amount of Li+ and W6+ ions. This work, therefore, proposes a novel strategy for the origin of piezoelectric properties and inspires doping of other heterovalent ions to improve the piezoelectric properties of ceramics. It further promotes the development of Pb-based piezoelectric ceramics for electromechanical devices that can efficiently operate under high-temperature environments.

Bandgap engineering and antiferroelectric stability of tantalum doped silver niobate ceramics from first-principles

Extensive research has been conducted on silver niobite (AgNbO3)-based antiferroelectric ceramics for their promising applications in energy storage applications, with various compositional modifications explored to improve their energy storage capabilities. In this theoretical study, we have systematically investigated the electronic, structural, and chemical bonding properties of AgNb1-xTaxO3 (x = 0.00, 0.125, 0.25, 0.375, 0.50, abbreviated as ANT100x) solid solutions based on first-principles calculation. Our results reveal that the bandgap increases from 1.82 eV to 1.89 eV, due to the higher energy level of Ta 5d orbitals compared to Nb 4d orbitals. The enlarged bandgap, accompanied with oxygen vacancy formation energy (ΔEf,vac), contributes to the enhancement of Eb. The Ta substitution of Nb site suppresses the cation displacement, oxygen octahedral distortion, and bond length and angles, indicating an improved stability of antiferroelectric phase. In addition, the electron localization function (ELF) and Bader charge values show weakened covalent bonding of Ta−O bonds compared to Nb−O bonds. These theoretical findings have the potential to aid in the advancement and creation of novel energy storage applications using lead-free AFE perovskites, as well as facilitate the manipulation of their breakdown electric field through bandgap engineering.

Bandgap Narrowing of BaTiO3-Based Ferroelectric Oxides through Cobalt Doping for Photovoltaic Applications.

Following the finding of power conversion efficiency above the Shockley-Queisser limit in BaTiO3 (BTO) crystals, ferroelectric oxides have attracted scientific interest in ferroelectric photovoltaics (FPV). However, since ferroelectric oxides have a huge bandgap (>3 eV), progress in this sector is constrained. This paper proposes and demonstrates a new ferroelectric BaTi1-xCoxO3 powder (0 ≤ x ≤ 0.08), abbreviated as BTCx, that exhibited a bandgap decrease with increased Co content. Notably, changing the composition from x = 0.0 to 0.08 caused the system to show a bandgap drop from 3.24 to 2.42 eV. The ideal design with x = 0.08 displayed an abnormal PV response. Raman spectroscopy measurements were used to investigate the cause of the bandgap decrease, and density functional theory was used to interpret the analyzed results. According to our findings, Co2+ doping and oxygen octahedral distortions enhance bandgap reduction. This research sheds light on how bandgap tuning developed and laid the way for investigating novel low-bandgap ferroelectric materials for developing next-generation photovoltaic applications.

Bandgap engineered BaTiO3-based ferroelectric oxides for photovoltaic applications

Ferroelectric oxides have gained research attention in the field of ferroelectric photovoltaics (PV) after the discovery of power conversion efficiency exceeding the Shockley–Queisser limit in BaTiO3 (BTO) crystals. However, advancement in this field is hindered by the wide bandgap (>3 eV) nature of ferroelectric oxides. In this work, a novel lead-free ferroelectric (1 − x)BTO − xBi(Ni2/3Nb1/3)O3 system was proposed and demonstrated to show bandgap reduction without compromising the polarization. Notably, the system displayed a bandgap reduction from 3.1 to 2.4 eV upon varying the composition from x = 0.0 to 0.05. Particularly, the optimal composition x = 0.02 showed enhancement in polarization (Pmax = 16 μC/cm2) and anomalous PV response with an open-circuit voltage of 6 V at 300 K. The origin of the bandgap reduction and polarization retention is explored experimentally by Raman spectroscopic measurements and analyzed theoretically by density functional theory. Our results revealed that the oxygen octahedral distortions and Ni2+ doping favor bandgap lowering, and Bi3+ ions stabilize the ferroelectric polarization. This study provides insight into the origin of bandgap tuning and paves the route for exploring new low-bandgap ferroelectric material with room temperature polarization.

Crystal structures, chemical bond, and microwave dielectric properties of Ba1-xKx(Zn1/3Nb2/3)O3-x/2 ceramics

Ba1-xKx(Zn1/3Nb2/3)O3-x/2 (BKZN, x = 0–0.2) ceramics were prepared by the high-temperature solid-state reaction method. Based on P–V–L theory, Raman vibration spectroscopy and X-ray photoelectron spectroscopy (XPS), this paper investigates the relationship between the internal and external factors of K+ substitution in the Ba(Zn1/3Nb2/3)O3 (BZN) ceramics and the microwave dielectric properties of the ceramics. X-ray diffraction (XRD) characterisation revealed that all samples were single phase with no impure phases. Replacing Ba2+ with K+ greatly reduced the sintering temperature and optimised the microwave dielectric properties of the ceramics. The dielectric constant (εr) was closely related to the ion polarizability and density, and inversely proportional to Raman shift of the A1g(O) peak. The quality factor (Q × f) depended largely on the lattice energy (Ub) and the full width at half-maximum (FWHM) of A1g(O) near 790 cm−1. The temperature coefficient of the resonance frequency (τf) could be inferred from the bond energy (Eb) and oxygen octahedral distortion. Finally, outstanding microwave dielectric properties (εr = 40.83, Q × f = 71,658 GHz and τf = 2.52 ppm/°C) were acquired for Ba0.95K0.05(Zn1/3Nb2/3)O2.975 ceramics sintered at the optimum sintering temperature (1325 °C) for 4 h.

Modification of BCZT piezoelectric ceramics by modulating oxygen vacancies in different sintering atmospheres

In this work, we regulated the oxygen vacancy concentration by sintering BCZT + 0.1 mol % Y + 0.1 mol % Nb [BCZT-0.1 mol % (Y + Nb)] ceramics under air, oxygen, argon, and vacuum atmospheres and examined the effect of oxygen vacancy concentration on phase composition, crystal structure, microstructure, and electrical properties. X-ray photoelectron spectrometry and X-ray diffraction Rietveld refinement showed that the air- and oxygen-sintered ceramic samples had lower oxygen vacancy concentrations, and the oxygen octahedral lattice distortion in the samples was stable when the R-O-T phases coexisted, forming a multiphase coexistence structure with more spontaneous polarization directions. The oxygen-sintering atmosphere is important in oxygen compensation, which promotes the formation of dense microstructure, thereby increasing the Curie temperature (TC). Oxygen vacancy formation energy was low in the argon and vacuum atmospheres, and some oxygen vacancies increased the mass transfer effect and grain growth. Nevertheless, excess oxygen vacancies increased the leakage current during polarization resulting in poor polarity, which prevents directional deflection of domains and degrades performance. The vacuum-sintered sample was calcined in 1000 °C air for oxygen supplementation sintering, and as the sintering time increased, the oxygen vacancy concentration decreased, the grains grew further, the density increased, and the piezoelectric properties improved. The oxygen-sintered BCZT-0.1 mol % (Y + Nb) samples had good comprehensive electrical properties (d33 = 547 pC/N, kp = 55%, εr = 5355, Pr = 10.63 µC/cm2, EC = 1.89 kV/cm, tan δ = 0.02, and TC = 102 °C).

Effect of Sb-induced oxygen octahedral distortion on piezoelectric performance and thermal stability of Pb(In,Nb)O3-Pb(Hf,Ti)O3 ceramics

The combination of excellent thermal stability and outstanding electrical performance is of great significance for piezoelectric ceramics. Herein, we have prepared 0.11Pb(In0.5Nb0.5)O3-0.89Pb(Hf0.47Ti0.53)O3-Sb2O5 (PIN-PHT-xSb) ceramics by solid-phase method and investigated the effect of oxygen octahedral lattice distortion on microstructure and macroscopic electrical properties. The distortion index of oxygen octahedra is studied by Rietveld refinement, showing that optimal octahedral distortion can soften B-O repulsion, disrupt long-range ordered ferroelectric domains, and enhance local heterogeneities, significantly increasing piezoelectric properties. Moreover, outstanding thermal stability and ultrahigh piezoelectric response of PIN-PHT-1.2Sb ceramics are realized under the synergistic influence of octahedral distortion, excellent density, and large grain size. Compared with PIN-PHT ceramics, PIN-PHT-1.2Sb ceramics exhibit ultrahigh piezoelectric responses (d33 = 706 pC/N, kp = 0.68, εr = 3244), a high Curie temperature (TC) of 300 °C, excellent thermal stability, and anti-fatigue properties.

Crystal Structure, Chemical Bond, and Microwave Dielectric Properties of Ba1-xSrx(Zn1/3Nb2/3)O3 Solid Solution Ceramics.

Ba1-xSrx(Zn1/3Nb2/3)O3 (BSZN) perovskite ceramics are prepared using the traditional solid-state reaction method. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to analyze the phase composition, crystal structure, and chemical states of BSZN ceramics, respectively. In addition, the dielectric polarizability, octahedral distortion, complex chemical bond theory, and PVL theory were investigated in detail. Systematic research showed that Sr2+ addition could considerably optimize the microwave dielectric properties of BSZN ceramics. The change in τf value in the negative direction was attributed to oxygen octahedral distortion and bond energy (Eb), and the optimal value of 1.26 ppm/°C was obtained at x = 0.2. The ionic polarizability and density played a decisive role in the dielectric constant, achieving a maximum of 45.25 for the sample with x = 0.2. The full width at half-maximum (FWHM) and lattice energy (Ub) jointly contributed to improving the Q × f value, and a higher Q × f value corresponded to a smaller FWHM value and a larger Ub value. Finally, excellent microwave dielectric properties (εr = 45.25, Q × f = 72,704 GHz, and τf = 1.26 ppm/°C) were obtained for Ba0.8Sr0.2(Zn1/3Nb2/3)O3 ceramics sintered at 1500 °C for 4 h.

High-Q×f value and temperature stable MgZrTa2O8 ceramics by Li heterovalent substitution

The Mg1-xLixZrTa2O8-x/2 (x = 0–0.07) ceramics were fabricated to investigate the effects of Li+ heterovalent substitution for Mg2+. The site occupancy and existence of the Li+ were examined based on Vienna Ab-initio Simulation Package (VASP) and X-ray photoelectron spectroscopy (XPS), respectively. Single phase solid solution with wolframite structure was identified in the whole region. Li+ substitution reduced the densification temperature from 1475 °C to 1400 °C. Notably, the Q×f exhibited an obvious increase by up to 74 % from 41,844 GHz at x = 0–72,782 GHz at x = 0.05. The Q×f for x < 0.01 was largely dependent on the intrinsic loss originating from packing fraction, while as 0.01 ≤ x ≤ 0.05, it was dominated by extrinsic factors, especially the oxygen vacancy concentration. The corresponding dielectric constant εr decreased in term of ionic polarizability. The variations of resonant frequency temperature coefficient τf were explained from the views of [TaO6] oxygen octahedral distortion and bond energy. A near-zero τf was obtained for x = 0.05 composition, accompanied by εr = 11.97, Q×f= 72,782 GH at 1450 °C. Li substitution was effective and inexpensive for MgZrTa2O8 ceramic to realize dielectric properties enhancement and densification temperature optimization simultaneously.

Magnetoelectric coupling at room temperature in LaTiO3/SrTiO3 heterojunctions

This work focuses on LaTiO3 (LTO) thin films synthesized by the polymeric precursor method and deposited onto SrTiO3 (STO) substrates via spin coating. The results show interesting coexisting ferromagnetic (Mr≈2.85 emu/g) - ferroelectric (Pr≈18.5 μC/cm2) responses at room temperature. Magnetoelectric coupling can be observed under DC bias magnetic field (14 V/cm.Oe), and its dielectric constant is affected by the coupling between magnetic and electric dipoles at room temperature as well as oxygen octahedra distortion along direction a. Little film-substrate mismatch significantly influences the system dielectric properties. Our results suggest the possibility to induce ferromagnetic/ferroelectric phases in the LTO/STO heterojunctions using an electric/magnetic field, respectively, due to the magnetoelectric coupling. This study also helps comprehend oxygen vacancy dynamics when applying a tensile strain or an external electric field, which is fundamental for actuators, switches, magnetic field sensors, and new types of electronic memory devices.

Oxygen octahedra distortion‐induced multiferroic properties of Er and Zr co‐doped BiFeO3 nanoparticles

AbstractThe present work unveiled the distortion of oxygen octahedra influencing magnetic and magnetoelectric properties of novel Bi1−xErxFe1−yZryO3 (x = 0, .05, .1, y = .02, .05) polycrystalline nanoparticles by sol–gel route. X‐ray diffraction patterns analysis reveals that pristine BiFeO3 and doped BiFeO3 are crystalized in the rhombohedral structure (R3c). The Fe–O–Fe bond angle of Bi1−xErxFe1−yZryO3 (x = 0, .05, .1, y = .02, .05) varies between 141° and 159.62° as the concentration of Er (via Bi site) and Zr (via Fe site) ions increases in BiFeO3. As a result, the tilt angle of oxygen octahedra and the canting angle of spiral spin arrangement increase. Hence, the maximum magnetization varies between .03144 and .37558 emu/g in Er and Zr co‐doped BiFeO3 system. The number of electrons per unit cell of Bi1−xErxFe1−yZryO3 (x = 0, .05, .1, y = .02, .05) lies between 733.38 and 831, respectively. Further, the number of coherently diffracting domains increases from 3.07 to 5.21, and then it decreases when Er and Zr are increased in BiFeO3. Consequently, the magnetoelectric coupling coefficient varies between .0265 and .2511 mV/cm Oe, respectively. Particularly, Bi0.95Er0.05Fe0.98Zr0.02O3 shows enhanced magnetic and magnetoelectric behaviors compared to other samples.

Correlating local chemical and structural order using Geographic Information Systems-based spatial statistics

Analysis of nanoscale short-range chemical and/or structural order via (scanning) transmission electron microscopy (S/TEM) imaging is fundamentally limited by projection of the three dimensional sample, which averages informational along the beam direction. Extracting statistically significant spatial correlations between the structure and chemistry determined from these two-dimensional datasets thus remains challenging. Here, we apply methods commonly used in Geographic Information Systems (GIS) to determine the spatial correlation between measures of local chemistry and structure from atomic-resolution STEM imaging of a compositionally complex relaxor, Pb(Mg1/3Nb2/3)O3 (PMN). The approach is used to determine the type of ordering present and to quantify the spatial variation of chemical order, oxygen octahedral distortions, and oxygen octahedral tilts. The extent of autocorrelation and inter-feature correlation among these short-range ordered regions are then evaluated through a spatial covariance analysis, showing correlation as a function of distance. The results demonstrate that integrating GIS tools for analyzing microscopy datasets can serve to unravel subtle relationships among chemical and structural features in complex materials that can be hidden when ignoring their spatial distributions.

Structure evolution of wolframite‐type ZnZrC2O8 (C = Nb, Ta) ceramics in relation to microwave dielectric properties

AbstractThe relationship among the sintering behavior, crystal structure, chemical bonding properties, and dielectric properties of wolframite‐type ZnZr(Nb1−xTax)2O8 (0.0 ≤ x ≤ 1.0) ceramics was investigated with the progressive replacement of Nb5+ by Ta5+. The optimum sintering temperature increases from 1225 to 1375°C with increasing Ta5+ content. The εr value falls from 27.34 to 22.34 due to a gradual decrease in bond ionicity and a shift in the Raman vibration modes toward higher wave numbers. The Q × f increases from 63 604 GHz (@6.71 GHz) to 115 631 GHz (@7.89 GHz), which is since the increase in the total lattice of chemical bonds. Moreover, the reduction in grain boundary area and the gradual lowering of the full width at half maximum of the Raman vibration modes contribute to the reduction in dielectric losses. First‐principles calculations illustrate that the growth in bandgap and electron cloud density in the internal space of the [Zn/ZrO6] octahedron leads to a reduction in dielectric loss. Furthermore, the reduced degree of oxygen octahedral distortion causes a change in τf from −46.56 to −37.40 ppm/°C.

Local Ionic Displacements and Polarization at the Paraelectric‐Ferroelectric Heterointerface: Effect of Octahedral Distortion

AbstractAt the ferroelectric ABO3 perovskite heterointerface, the broken translational symmetry significantly alters the octahedral network and cation sublattices. Experimentally revealing the interaction between the polarization and atomic structure parameters is beneficial not only for understanding the novel physical phenomena but also for realizing exotic physical functionalities at the materials surface science. Here, it is demonstrated that the induced polarization can be realized by the cooperative interaction between the octahedral distortion and the cation sublattices at the paraelectric‐ferroelectric heterointerface in the (K,Na)NbO3 epitaxial thin film. It is found that the cation–cation displacement scales with the tetragonality of the perovskite unit cell but not with the polarization, which is minimal in the substrate but increases substantially in the thin film. Nevertheless, the oxygen octahedral distortion in the substrate, accompanied by octahedral rotation, is stronger than that in the film, resulting in a translated and stable polarization across the interface. These results demonstrate the octahedral network plays a significant role in the ferroelectric polarization and can also greatly advance the understanding of the heterointerface science for ferroelectrics.

Origin of giant electric-field-induced strain in faulted alkali niobate films

A large electromechanical response in ferroelectrics is highly desirable for developing high-performance sensors and actuators. Enhanced electromechanical coupling in ferroelectrics is usually obtained at morphotropic phase boundaries requiring stoichiometric control of complex compositions. Recently it was shown that giant piezoelectricity can be obtained in films with nanopillar structures. Here, we elucidate its origin in terms of atomic structure and demonstrate a different system with a greatly enhanced response. This is in non-stoichiometric potassium sodium niobate epitaxial thin films with a high density of self-assembled planar faults. A giant piezoelectric coefficient of ∼1900 picometer per volt is demonstrated at 1 kHz, which is almost double the highest ever reported effective piezoelectric response in any existing thin films. The large oxygen octahedral distortions and the coupling between the structural distortion and polarization orientation mediated by charge redistribution at the planar faults enable the giant electric-field-induced strain. Our findings demonstrate an important mechanism for realizing the unprecedentedly giant electromechanical coupling and can be extended to many other material functions by engineering lattice faults in non-stoichiometric compositions.

Crystal structure and microwave dielectric properties of (Mg0.2Ni0.2Zn0.2Co0.2Mn0.2)2SiO4 - A novel high-entropy ceramic

Novel (Mg0.2Ni0.2Zn0.2Co0.2Mn0.2)2SiO4 (A5SO) high-entropy microwave dielectric ceramics with olivine structure were prepared in the sintering temperature range of 1100 °C–1300 °C via the solid-phase reaction route. The crystal structure was confirmed by XRD, Raman, and Rietveld refinement. Optimal microwave dielectric properties (εr = 8.02, tanδ = 0.00051 at 14.5 GHz, and τf = −38.2 ppm/°C) were obtained at the sintering temperature of 1250 °C, where a relative density of 95.1% was detected. The complex chemical bonding theory manifests that the εr value of A5SO is mainly affected by the ionicity of A-O (A = Mg, Ni, Zn, Co, Mn) bond, while the dielectric loss is affected by both A-O and Si–O lattice energy. The τf value is mainly influenced by the [A(2)O6] oxygen octahedral distortion (1.8 × 10−3). The experimental results of this study provide both theoretical and practical guidance for high-entropy microwave dielectric ceramic applications.

Tunable Magnetic Anisotropy in Patterned SrRuO3 Quantum Structures: Competition between Lattice Anisotropy and Oxygen Octahedral Rotation

AbstractArtificial perovskite oxide nanostructures possess intriguing magnetic properties due to their tailorable electron–electron interactions, which are extremely sensitive to the oxygen coordination environment. To date, perovskite oxide nanodots with sizes below 50 nm have rarely been reported. Furthermore, the oxygen octahedral distortion and its relation to magnetic properties in perovskite oxide nanodots remain unexplored thus far. Here, the magnetic anisotropy in patterned SrRuO3 (SRO) nanodots as small as 30 nm are studied. The constituent elements, in particular oxygen ions, are directly visualized via performing atomic resolution electron microscopy and spectroscopy. It is observed that the magnetic anisotropy and RuO6 octahedra distortion in SRO nanodots are both nanodot size‐dependent but remain unchanged in the first 3‐unit‐cell interfacial SRO monolayers regardless of the dots’ size. Combined with first principle calculations, a unique structural mechanism behind the nanodots’ size‐dependent magnetic anisotropy in SRO nanodots is unraveled, suggesting that the competition between lattice anisotropy and oxygen octahedral rotation mediates anisotropic exchange interactions in SRO nanodots. These findings demonstrate a new avenue toward tuning magnetic properties of correlated perovskite oxides and imply that patterned nanodots could be a promising playground for engineering emergent functional behaviors.

Local-electrostatics-induced oxygen octahedral distortion in perovskite oxides and insight into the structure of Ruddlesden\u2013Popper phases

As the physical properties of ABX3 perovskite-based oxides strongly depend on the geometry of oxygen octahedra containing transition-metal cations, precise identification of the distortion, tilt, and rotation of the octahedra is an essential step toward understanding the structure–property correlation. Here we discover an important electrostatic origin responsible for remarkable Jahn–Teller-type tetragonal distortion of oxygen octahedra during atomic-level direct observation of two-dimensional [AX] interleaved shear faults in five different perovskite-type materials, SrTiO3, BaCeO3, LaCoO3, LaNiO3, and CsPbBr3. When the [AX] sublayer has a net charge, for example [LaO]+ in LaCoO3 and LaNiO3, substantial tetragonal elongation of oxygen octahedra at the fault plane is observed and this screens the strong repulsion between the consecutive [LaO]+ layers. Moreover, our findings on the distortion induced by local charge are identified to be a general structural feature in lanthanide-based An + 1BnX3n + 1-type Ruddlesden–Popper (RP) oxides with charged [LnO]+ (Ln = La, Pr, Nd, Eu, and Gd) sublayers, among more than 80 RP oxides and halides with high symmetry. The present study thus demonstrates that the local uneven electrostatics is a crucial factor significantly affecting the crystal structure of complex oxides.

Octahedral rotations trigger electronic and magnetic transitions in strontium manganate under volume expansion

The perovskite structure of manganate yields a series of intriguing physical properties. Based on the results of first-principles calculations, strontium manganate appears to undergo a magnetic phase transition and a metal–insulator transition—from antiferromagnetic insulator to ferromagnetic metal and then to ferromagnetic insulator—under isotropic volume expansion combined with oxygen octahedral distortions. Interestingly, the results show that increasing the Mn–O bond length and adding rotation of the oxygen octahedra can soften the breathing distortion and account for the insulator phase. We further build a simple model to explain such transitions. Due to electron transfer and the favoring of a hole state of ligand p orbitals, the electron state transfer from to and then to . Such rearrangement of charges is responsible for the transitions of its magnetic order and electronic structure. Furthermore, we calculate spin susceptibility under the bare conditions and random phase approximation. The magnetic order of the intermediate metal state of itinerant electrons behaves as a ferromagnetic.

Enhanced hybrid improper ferroelectricity in Fe/Nb cosubstituted Ca3Mn2O7 ceramics

AbstractThe prototypical Ruddlesden‐Popper compound Ca3Mn2O7 has been predicted to possess hybrid improper ferroelectricity, where the polarization is induced by the condensation of two oxygen octahedral distortion modes. Nevertheless, it is a big challenge to switch the polarization at room temperature in Ca3Mn2O7 since the presence of intermediate nonpolar Acaa phase generally leads to the complex domain morphology. Here, the effects of Fe/Nb cosubstitution on hybrid improper ferroelectricity in Ca3Mn2O7 are reported, and easy polarization switching at room temperature is achieved in Ca3[Mn0.5(Fe0.5Nb0.5)0.5]2O7. The ferroelectric phase transition occurs directly from I4/mmm to A21am at a temperature far above room temperature without intermediate nonpolar Acaa phase. The distinct transition pathway forms the alternating 180°‐type ferroelectric domains rather than the irregular 90°‐type ferroelastic domains stacked along [001], resulting in easy polarization switching at room temperature. Moreover the enhanced ferroelectric polarization (Pr ~2.0 μC/cm2) is obtained due to the increased anti‐ferrodistortive displacements of Ca cations at A‐site, arising from the larger amplitudes of oxygen octahedral distortions. Chemical pressure is emphasized here for the tunability of phase transition, domain morphology, and ferroelectric characteristics, and it provides a useful approach for designing and creating high‐performance improper ferroelectrics.