Recent Progress of Hybrid Improper Ferroelectrics with Ruddlesden-Popper Structure

doi:10.15541/jim20240521

Abstract

Abstract:

Hybrid improper ferroelectricity (HIF) is recognized as a secondary ferroelectric phenomenon induced by coupling of in-plane rotation and out-of-plane tilt of anion octahedra in compounds with the units of perovskite structure. HIF is expected to be applicable in the multiferroic materials with strong magnetoelectric coupling owing to its intrinsic characteristic for electric-field control of magnetism, thereby greatly extending the connotation and denotation of ferroelectric physics. This paper focuses on the experimental progress of HIF materials with Ruddlesden-Popper (R-P) structure. It also establishes the linear relationship between Curie temperature (T_C) and tolerance factor (τ) of double-layered R-P oxides, elucidating the underlying physical mechanisms of HIF. Based on intrinsic electric-field control of magnetism for HIF, the detection of coexistence of polar and weak ferromagnetic phases in ferrites with double-layered R-P structures is of great scientific significance. Additionally, the documented ferroelectricity in the A-site cation-ordered triple-layered R-P oxide has significantly expanded the fields of HIF. Although significant progress has been achieved in understanding HIF in R-P oxides, more efforts should be made to explore more new material systems and single-phase multiferroic materials.

Key words: hybrid improper ferroelectricity, Ruddlesden-Popper structure, single-phase multiferroicity, review

CLC Number:

O482

ZHANG Bihui, LIU Xiaoqiang, CHEN Xiangming. Recent Progress of Hybrid Improper Ferroelectrics with Ruddlesden-Popper Structure[J]. Journal of Inorganic Materials, 2025, 40(6): 587-608.

Figures/Tables 17

Fig. 1 (a) Summary of multifunctional properties in HIF with R-P structure; (b) Number of articles published on R-P oxides in recent years based on the Web of Science database

Fig. 2 Energetics of a transition from paraelectric to ferroelectric phase for (a) proper and (b) improper ferroelectric system[23] F represents thermodynamic free energy of the system, η represents atomic polarity displacement, and T represents temperature. The black line represents the free energy of T>TC, and the minimum value of the free energy is at η=0, indicating that it is a paraelectric phase. The red line indicates the free energy of T<TC, and the minimum value of the free energy is at η≠0, indicating that it is a ferroelectric phase. The three lines between black and red indicate the transition state between the paraelectric phase and the ferroelectric phase. Colorful figure is available on website.

Fig. 3 Symmetry mode decomposition of the (a) paraelectric to (b) ferroelectric structure in R-P A′2AB2O7, and (c) representation of anti-ferrodistortive displacements (X) at every layer and total ferroelectric polarization (Ptotal) in ferroelectric structure[25]

Fig. 4 (a) Ferroelectric a−a−c+ structure of A3B2O7 R-P phase; (b) First principles amplitudes of two octahedral rotations and induced polar mode for a suite of A3B2O7 materials, arranged by increasing τ of ABO3 parent[26]

Fig. 5 (a, b) Schematic diagrams of two octahedral tilt modes of a0a0c+and a−a−c0 of (Ca,Sr)3Ti2O7 single crystal; (c) Photographic and (d) circular differential interference contrast image of a cleaved (001) surface of Ca2.46Sr0.54Ti2O7 single crystal; (e) Ferroelectric hysteresis loops of Ca3−xSrxTi2O7 (x=0, 0.54, 0.85) single crystal along [110] orientation; (f) Schematic picture of IP-PFM measurement[49]

Table 1 Parameters regarding ferroelectric properties of Ca3Ti2O7-based oxides with double-layered R-P structure[43-44,49,64,70 -73,79 -81]

Compound		τ	P_r/(μC·cm^-2)	E_c/(kV·cm^-1)	T_C/K	Ref.
Ca₃Ti₂O₇	Ceramic	0.8465	0.9	110	1085	[64]
Ca₃Ti₂O₇	Sol-Gel ceramic	0.8465	4.32	108	1046	[80]
Ca₃Ti₂O₇	Two-step ceramic	0.8465	1.32	78	—	[79]
Ca₃Ti₂O₇	Film	0.8465	8	5	—	[81]
Ca₃Ti₂O₇	Single crystal	0.8465	8	150	—	[49]
Ca_2.9Sr_0.1Ti₂O₇	Ceramic	0.8487	0.5	210	1034	[73]
Ca_2.8Sr_0.2Ti₂O₇	Ceramic	0.8508	0.2	190	970	[73]
Ca_2.7Sr_0.3Ti₂O₇	Ceramic	0.8529	0.12	185	940	[73]
Ca_2.6Sr_0.4Ti₂O₇	Ceramic	0.8550	0.1	170	850	[73]
Ca_2.46Sr_0.54Ti₂O₇	Single crystal	0.8580	0.54	150	—	[49]
Ca_2.15Sr_0.85Ti₂O₇	Single crystal	0.8645	0.85	180	—	[49]
Ca₃Ti_1.9Mn_0.1O₇	Ceramic	0.8481	0.6	122	1075	[43]
Ca₃Ti_1.8Mn_0.2O₇	Ceramic	0.8497	0.4	145	1030	[43]
Ca₃Ti_1.7Mn_0.3O₇	Ceramic	0.8513	0.3	150	1000	[43]
Ca₃Ti_1.8Al_0.1Nb_0.1O₇	Ceramic	0.8472	1.24	160	1082	[44]
Ca₃Ti_1.8Al_0.1Nb_0.1O₇	Ceramic	0.8453	0.5	130	1099	[44]
Ca₃Ti_1.9Al_0.1O_6.95	Ceramic	0.8480	0.5	130	973	[44]
Ca_2.9La_0.1Ti_1.9Al_0.1O₇	Ceramic	0.8484	0.39	115	950	[64]
Ca_2.8La_0.2Ti_1.8Al_0.2O₇	Ceramic	0.8503	0.17	117	797	[64]
Ca_2.7La_0.3Ti_1.7Al_0.3O₇	Ceramic	0.8521	0.16	120	645	[64]
Ca_2.85Na_0.15Ti₂O₇	Ceramic	0.8469	0.2	50	—	[71]
Ca_2.99Na_0.01Ti₂O₇	Ceramic	0.8466	0.5	80	—	[72]
Ca_2.9Ru_0.1Ti₂O₇	Ceramic	0.8428	4.4	100	—	[70]

Fig. 6 Comparison of ferroelectric properties for Ca3Ti2O7-based compounds with double-layered R-P structure[40]

Fig. 7 (a) DF-TEM image obtained at room temperature (RT) using the g=100 diffraction spot showing the ferroelectric domains, with blue and red arrows indicating directions of ferroelectric polarization along [100]; (b) DF-TEM image obtained at RT using the reflection g=220; (c) PFM measurements for Ca3[Mn0.5(Fe0.5Nb0.5)0.5]2O7 ceramics at RT: mappings of topography, amplitude contrast, phase contrast, and contact resonant frequency; (d) First and second harmonic responses versus AC voltage; (e, f) Local switching spectroscopy for (e) amplitude voltage butterfly loops and (f) phase voltage hysteresis loops under various DC bias[45]

Fig. 8 Comparison of ferroelectric properties for Sr-based oxides with R-P structure (Sr3Sn2O7 single crystal[112], (Sr,Ba)3Sn2O7 ceramics[84], (Sr,Ca)3Sn2O7 ceramics[85], (Sr,Ba)3Zr2O7 ceramics[86], and Sr3(Sn,Zr)2O7 ceramics[113])

Fig. 9 (a) Crystal structures of four phases observed experimentally for Sr3Sn2O7, specified by space group symmetry and Glazer tilt notation[118]; (b) Phase diagram of Sr3Sn2O7 established in the present study[118]; (c) Calculated layer-resolved polarization using a point-charge approximation for the crystal structure refined against NPD data at 300 K (left panel), [010] projected crystal structure (right panel) with Sr, Zr, and O atoms in gray, blue, and red, respectively[119]; (d) Atomic contributions and layer-by-layer contributions to polarization in Sr3Hf2O7, in which Sr1-O represents the SrO layer between perovskite layers, and Sr2-O represents the SrO layer between rock-salt and perovskite layers[120]

Fig. 10 TC of double-layered R-P ferroelectrics against τ of their perovskite unit[40]

Fig. 11 Dependence of dielectric constant on temperature and ferroelectric phase transition schematic of Li2Sr(Nb1−xTax)2O7 oxides[65]

Fig. 12 (a) Crystal structures, room temperature P-E loops and the A-site cation ordering dependence of DFT calculated energy for La2SrSc2O7 ceramics[123]; (b) P-E loops for La2Sr(Sc1−xFex)2O7 ceramics under a electric field of 400 kV/cm and a frequency of 2 Hz[121] ; (c) Temperature dependence of dielectric constant for La2Sr(Sc1−xFex)2O7 ceramics over the temperature range of 150-600 K during heating and cooling processes[121]; (d) Temperature dependence of DC magnetic susceptibility of La2Sr(Sc1−xFex)2O7 (x=0.15) ceramics, with inset showing Curie-Weiss fitting results[121]; (e) Isothermal field dependence of magnetization of La2Sr(Sc1−xFex)2O7 (x=0.15) ceramics at various temperatures[121]

Fig. 13 Comparison of ferroelectric properties of double-layered R-P materials (Ca3Ti2O7 ceramics[80], Sr3Sn2O7 ceramics[84], Sr3Zr2O7 ceramics[86], Li2CaTa2O7 ceramics[26], and Li2SrNb2O7 ceramics[130]) (a) Tolerance factor; (b) Curie temperature; (c) Remnant polarization; (d) Coercive field

Fig. 14 (a) Phase diagram of (1−x)(CaySr1−y)1.15Tb1.85Fe2O7-xCa3Ti2O7 (0≤x≤0.3, y=0.60); (b) Ferroelectric polarization and saturated magnetic moment versus composition; (c) Linear magnetoelectric susceptibility versus composition at 60 and 100 K[136]

Fig. 15 (a) Crystal structure of several oxides with single layer R-P structure[143]; (b) Schematic diagram of the intercalation structure of HRTiO4 and NaRTiO4[139]; (c, d) Temperature dependence of SHG for (c) AASmTiO4 and (d) AAEuTiO4 with AA representing Na (yellow circles) and K (purple circles)[141]

Fig. 16 (a) Room temperature P−E loop and J−E curves measured at 390 kV/cm by PUND method[149]; (b) Calculated energies for Li2La2Ti3O10 with different crystal symmetries in the triple-layered R-P structure relative to the lowest energy Pc phase at 0 K[149]; (c) Room temperature P−E loops of Li2Nd2Ti3O10 ceramics measured through PUND method[150]; (d) Rotation (θR) and tilt (θT) angles of Li2La2Ti3O10 (LLTO) and Li2Nd2Ti3O10 (LNTO) ceramics, respectively[150]; (e) Schematic diagrams of crystal structures for Li2La2Ti3O10 ceramics based on the Rietveld refinement (the green, brown, and red balls represent Li+, La3+, and O2− ions, respectively, while Ti4+ cations reside in the oxygen octahedra center)[149]; (f) Layer-by-layer contributions to polarization in Li2La2Ti3O10 calculated by the Born effective charge mode[149]

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