Transformation from insulating p-type to semiconducting n-type conduction in CaCu3Ti4O12-related Na(Cu5/2Ti1/2)Ti4O12 ceramics

Abstract

A double doping mechanism of Na+ + ½ Ti4+ → Ca2+ + ½ Cu2+ on the general formula Ca1−xNax(Cu3−x/2Tix/2)Ti4O12 has been used to prepare a series of isostructural CaCu3Ti4O12 (CCTO)-type perovskites. A complete solid solution exists for 0 ≤ x ≤ 1 and all compositions exhibit incipient ferroelectric behaviour with higher than expected intrinsic relative permittivity. Although CCTO ceramics typically exhibit n-type semiconductivity (room temperature, RT, resistivity of ∼10–100 Ω cm), Na(Cu5/2Ti1/2)Ti4O12 (NCTO) ceramics sintered at 950 °C consist of two insulating bulk phases (RT resistivity > 1 GΩ cm), one p-type and the other n-type. With increasing sintering temperature/period, the p-type phase transforms into the n-type phase. During the transformation, the resistivity and activation energy for electrical conduction (Ea ∼ 1.0 eV) of the p-type phase remain unchanged, whereas the n-type phase becomes increasingly conductive with Ea decreasing from ∼ 0.71 to 0.11 eV with increasing sintering temperature. These changes are attributed to small variations in stoichiometry that occur during high temperature ceramic processing with oxygen-loss playing a crucial role.

Good dielectric performance and broadband dielectric polarization in Ag, Nb co‐doped TiO2

“…In order to evaluate the temperature stability, we calculated the change rate of dielectric constant with temperature at different frequencies (Δ ε r / ε 25°C ), as shown in Figure 5B. The results show that the temperature stability value of ANTO0.005 and ANTO0.01 ceramics is stable between ±15% at the temperature range from 83 to 473 K, which satisfies X9R (−55°C–200°C, Δ ε r / ε 25°C < ±15%) and X8R (−55°C–150°C, Δ ε r / ε 25°C < ±15%) requirements for the temperature range of application and is much better than that of NiO‐based oxides, e.g., La 2− x Sr x NiO 4 and CaCu 3 Ti 4 O 12 ceramics 26‐28 . Furthermore, it is worth noting that the high dielectric permittivity of ANTO x ceramics is still maintained even when the temperature is lowered to 83 K.…”

Improved giant dielectric properties of CaCu3Ti4O12via simultaneously tuning the electrical properties of grains and grain boundaries by F− substitution

“…25 For this point of view, it was proposed that the GB region may possess a p-type semiconductor nature, resulting from high oxygen content and/ or vacancies of metal ions along the GBs compared with the ntype semiconductor nature inside the grains. 50 For CCTOF ceramics, the creation of oxygen vacancies may possibly be inhibited (or decreased) by F À doping anions due to the lower valence state of the dopant, retaining the p-type semiconductor nature of the GBs and potential barrier height. Thus, substitution of F À anions not only decreased the possibility of a reduction in F B as a result of creation of oxygen vacancies, but it also enhanced F B resulting from the creation of free charges inside the semiconducting grains.…”

Good thermal stability, giant permittivity, and low dielectric loss for X9R‐type (Ag1/4Nb3/4)0.005Ti0.995O2 ceramics

“…The tanδ values of the sample at 1 and 10 kHz are lower than 0.07 in the temperature range from −60 to 120°C, as shown in the inset of Figure C. The ε r value is almost independent of temperature and remains at ~9000 in the temperature range from −80 to 240°C, which is far superior to that of CaCu 3 Ti 4 O 12 , La 2‐x Sr x NiO 4 ,and NiO‐based oxides . When the temperature is above 240°C, the ε r values are apparently dependent on temperature.…”

“…At 1 kHz, the value of the temperature coefficient is stable at 13.7% even though the temperature reaches up to 200°C. This good thermal stability is much better than other giant permittivity materials . Consequently, the especially good thermal stability of (Ag 1/4 Nb 3/4 ) 0.005 Ti 0.995 O 2 ceramics satisfies the condition (Δ ε r / ε 25°C < ±15%) for its practical application in X9R capacitor, for which it is expected to be used extensively.…”

“…In the past decades, giant permittivity materials with a large dielectric constant ( ε r ), low dielectric loss (tanδ), and good thermal stability have attracted much attention due to the requirements for the miniaturization of electronic devices and high‐energy storage capacitors . In 2013, the remarkable dielectric behavior of the materials, In and Nb codoped TiO 2 ‐based ceramics, was reported by Liu et al; these materials showed low dielectric loss (<5%) and large dielectric constant (~10 4 ) and had better temperature stability in the range from 80 to 450 K. Meanwhile, the authors deemed that the origin of the dielectric response was attributed to the intrinsic dielectric effect, that is, the electron pinned defect dipole (EPDD).…”