Electrical Conductivity of Piezoelectric Strontium Bismuth Titanate Under Controlled Oxygen Partial Pressure

Abstract

Hysteresis free and linear piezoelectric behavior of SrBi4Ti4O15 (SrBIT) is very promising for precise sensors/actuators devices. Despite a quite low longitudinal piezoelectric coefficient (around 15 pC/N), its elevated ferroelectric phase transition temperature (540°C) allows its use above 300°C. Electrical conductivity at such temperatures should be kept as low as possible in order to avoid loss of piezoelectric properties or charge drifts. Under reducing conditions, however, the electrical conductivity may change considerably. The electrical conductivity of SrBi4Ti4O15 (SrBIT) has been measured under controlled oxygen partial pressure at elevated temperatures (700-900°C) from 1 atm down to 10−15atm. From 1 atm down to 10−15 atm pO2, above 700°C, the conductivity of SrBIT exhibits a -1/4 slope in log-log scale indicating n-type conductivity and an impurity controlled oxygen vacancy concentration. A conductivity minimum is observed around 0.2 atm for undoped SrBIT at 800°C. Acceptor doping (Mn) raises the minimum and flattens the conductivity curve with slope around -1/10 at 700°C, and -1/6 at 900°C. Ionic conductivity and defect ionization are discussed to account for this. Preliminary results indicate the possibility of a large, pO2 independent, region, down to 10−15atm pO2. The ionic transport number was found to be 0.42 at 800°C for undoped SrBIT and 0.75 for Mn doped SrBIT. The activation energies of undoped (1.35 eV) and Mn doped (1.44 eV) samples are close to each other as expected for a common mechanism

Development of a High-Throughput Screening Method for Oxide-Ion Conductors and Its Application to Bismuth-Based Oxide Library Thin Films

“…27−29 Many of these compounds have rarely been studied as OICs until now. However, as part of a dielectric investigation, the conductivities of the bismuth-layered compounds SrBi 2 Ti 2 O 5 (SBT), SrBi 2 Nb 2 O 9 (SBN), and SrBi 4 Ti 4 O 15 (SBIT) have been reported, 30−32 of which SBIT is a mixed conductor, 30 and SBT has the potential for high oxide-ion conductivity by adding acceptor dopants. 31,32 Despite the aforementioned interest in bismuth-layered compounds, how composition influences conductivity has yet to be studied sufficiently.…”

“…Bismuth-layered compounds have the general formula (Bi 2 O 2 ) 2+ (A m –1 B m O 3 m+1 ) 2– and are ferroelectrics with various compositions depending on the stacking number m of (Bi 2 O 2 ) 2+ blocks and the types of cations A and B. − Many of these compounds have rarely been studied as OICs until now. However, as part of a dielectric investigation, the conductivities of the bismuth-layered compounds SrBi 2 Ti 2 O 5 (SBT), SrBi 2 Nb 2 O 9 (SBN), and SrBi 4 Ti 4 O 15 (SBIT) have been reported, − of which SBIT is a mixed conductor, and SBT has the potential for high oxide-ion conductivity by adding acceptor dopants. , …”