Probing ferroelectricity in highly conducting materials through their elastic response: Persistence of ferroelectricity in metallic BaTiO3−δ

Abstract

The question whether ferroelectricity (FE) may coexist with a metallic or highly conducting state, or rather it must be suppressed by the screening from the free charges, is the focus of a rapidly increasing number of theoretical studies and is finally receiving positive experimental responses. The issue is closely related to the thermoelectric and multiferroic (also magnetic) applications of FE materials, where the electrical conductivity is required or spurious. In these circumstances, the traditional methods for probing ferroelectricity are hampered or made totally ineffective by the free charges, which screen the polar response to an external electric field. This fact may explain why more than 40 years passed between the first proposals of FE metals and the present experimental and theoretical activity. The measurement of the elastic moduli, Young's modulus in the present case, versus temperature is an effective method for studying the influence of doping on a FE transition because the elastic properties are unaffected by electrical conductivity. In this manner, it is shown that the FE transitions of BaTiO 3−δ are not suppressed by electron doping through O vacancies; only the onset temperatures are depressed, but the magnitudes of the softenings, and hence of the piezoelectric activity, are initially even increased.

Resistive Switching and Redox Process at the BaTiO3/(La,Sr)MnO3 Multiferroic‐Type Interface

“…Although such defects may alter the insulating character of BTO (and compromise the use of traditional methods for probing ferroelectricity), their presence cannot suppress its ferroelectric character. [ 45–46 ]…”

“…Although such defects may alter the insulating character of BTO (and compromise the use of traditional methods for probing ferroelectricity), their presence cannot suppress its ferroelectric character. [45][46] Figure 1c shows the random Rutherford backscattering spectrometry (RBS) spectrum corresponding to the sample of Figure 1a. By measuring the energy distribution and yield of the backscattered He + ions, the total atom number of each element per surface unit may be determined.…”

Two-dimensional polar metals in KNbO3/BaTiO3 superlattices: first-principle calculations

“…Analogous to metal-based polar metals with structural phase transitions, [3][4][5][6][7][8][9][10][11][12] ferroelectric-based polar metals are another category of polar metals with insulatormetal transitions. [13][14][15][16][17][18][19][20] Compared with the structural phase transitions hardly occurred in metals, insulator-metal transitions are prone to be realized in ferroelectrics, and they have broad practical application prospects due to the enormous range of ferroelectrics and their compounds readily available at room temperature. A conventional approach to achieve metal behavior in ferroelectrics is to introduce electron carriers into the ferroelectrics by injecting vacancies or doping, [13][14][15][16][17][18][19] e.g., O vacancies in BTO, 13,14 element or electrostatic doping in BTO.…”

“…[13][14][15][16][17][18][19][20] Compared with the structural phase transitions hardly occurred in metals, insulator-metal transitions are prone to be realized in ferroelectrics, and they have broad practical application prospects due to the enormous range of ferroelectrics and their compounds readily available at room temperature. A conventional approach to achieve metal behavior in ferroelectrics is to introduce electron carriers into the ferroelectrics by injecting vacancies or doping, [13][14][15][16][17][18][19] e.g., O vacancies in BTO, 13,14 element or electrostatic doping in BTO. [15][16][17][18][19] The polarization displacements show a rapid decrease with increasing carrier concentration.…”

Unveiling the high-temperature dielectric response of $$\text {Bi}_{0.5}\text {Na}_{0.5}\text {TiO}_{3}$$

“…In last years, the analysis of the elastic constants and energy dissipation spectra of electroceramics materials by mechanical spectroscopy has been providing clear information about the occurrence and characteristics of phase transitions 16,22,[37][38][39][40][41] , especially in materials with ferroelastic nature like BNT, relaxation mechanisms [42][43][44] and defects mobility [44][45][46] . Nevertheless, only a few works in the literature address the use of this technique to investigate the phase transitions and other thermally stimulated processes in BNT-based materials 11,22,24,[47][48][49] .…”