# Reasons for the High Electrical Conductivity of Bismuth Ferrite and Ways to Minimize It
## 2 Materials and Methods  
The objects of study were solid solutions (SS) of the Bi\({}_{1-x}\)REE\({}_{x}\)FeO\({}_{3}\) composition (REE, lanthanides, Ln: La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tu, Yb, Lu; \(x\) = 0.0-0.5; \(\Delta x\) = 0.025, 0.05, 0.10). The main method for preparing studied SS was solid-phase synthesis with intermediate grinding and granulation of dispersed crystalline powders and subsequent sintering using conventional ceramic technology (without externally applied pressure). Optimum technological procedures ensuring the purity (or the minimum number of ballast phases), experimental density close to the theoretical one, and the integrity of ceramics were chosen on a series of the samples of each composition, varying temperature, duration and frequency of firing. Specific modes of the synthesis and sintering of the SS were: T\({}_{1}\) = (1060 \(\div\) 1180) K, \(\tau_{1}\) = (5 \(\div\) 10) hours; T\({}_{2}\) = (1070 \(\div\) 1180) K, \(\tau_{2}\) = (5 \(\div\) 10) hours, T\({}_{\rm{sint}}\) = (1140 \(\div\) 1270) K, \(\tau_{\rm{sint}}\) = 2 h (depending on the composition). Technological regimes for the preparing of studied SS are presented in [11]. Some SS were subjected to mechanically activating procedures performed with the help of a planetary mill of the AGO-2 brand. Before sintering the samples, the powders were formed in the shape of columns with a diameter of 12 mm and a height of 20 mm. Sintered ceramic billets were machined (plane cutting, grinding on flat surfaces and ends) in order to obtain measuring samples with a diameter of 10 mm and a height of 1 mm. Each composition of such samples contained (5 \(\div\) 10) pieces. Before metallization, the samples were calcined at a temperature of T\({}_{\rm{calc}}\) = 770 K for 0.5 h to remove residual organic substances and degrease surfaces in order to increase the adhesion of the metal coating with ceramics. The electrodes were applied by double burning of a silver-containing paste at a temperature of 1070 K for 0.5 h.  
X-ray diffraction studies at room temperature were performed by powder diffraction using DRON-3 and ADP-1 diffractometers (Cox\(\alpha\)-radiation; Mn-filter; Bragg-Brentano focusing scheme). We studied bulk and ground ceramic objects, which allowed us to exclude the influence of the surface effects, strength and textures that arise in the process of obtaining ceramics. The calculation of the structural parameters was performed according to a standard method. X-ray density (\(\varrho_{\rm{X-ray}}\)) was determined by the formula: \(\varrho_{\rm{X-ray}}=1.66\cdot M/V\), where \(M\) is the weight of the formula unit in grams, \(V\) is the volume of the perovskite cell in A. The measurement errors of the structural parameters were as follows: linear \(\Delta a=\Delta b=\Delta c=\pm(0.002\div 0.004)\) A; angular \(\Delta\alpha=3\)'; and volume \(\Delta V=\pm 0.05\)A\({}^{3}\) (\(\Delta V/V\cdot 100\%=0.07\%\)). The experimental (\(\epsilon_{\rm exp}\)) density of the samples was determined by hydrostatic weighing, where octane was used as a liquid medium. The relative density (\(\epsilon_{\rm rel}\)) was calculated by the formula: (\(\epsilon_{\rm exp}/\varrho_{\rm X-ray}\))\(\cdot 100\%\). Densities of the studied SS are presented in [12]. The real and imaginary parts of the relative permittivity and dielectric loss tangent (\(\varepsilon^{\prime}/\varepsilon_{0}\), \(\varepsilon^{\prime\prime}/\varepsilon_{0}\), \(\rm{tg}\delta\)) at frequencies of (20-2\(\cdot 10^{6}\)) were studied on a special bench using a precision LCR- meter of Agilent E4980A in the intervals of (300-900) K temperatures. The electrical resistance R (Ohm) was measured at direct current at room temperature using an Agilent 4339B High Resistance Meter.