scholarly journals Formation of Solid Solutions and Physicochemical Properties of the High-Entropy Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ (Ln = La, Pr, Nd, Sm or Gd) Perovskites

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5264
Author(s):  
Juliusz Dąbrowa ◽  
Klaudia Zielińska ◽  
Anna Stępień ◽  
Marek Zajusz ◽  
Margarita Nowakowska ◽  
...  

Phase composition, crystal structure, and selected physicochemical properties of the high entropy Ln(Co,Cr,Fe,Mn,Ni)O3−δ (Ln = La, Pr, Gd, Nd, Sm) perovskites, as well as the possibility of Sr doping in Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ series, are reported is this work. With the use of the Pechini method, all undoped compositions are successfully synthesized. The samples exhibit distorted, orthorhombic or rhombohedral crystal structure, and a linear correlation is observed between the ionic radius of Ln and the value of the quasi-cubic perovskite lattice constant. The oxides show moderate thermal expansion, with a lack of visible contribution from the chemical expansion effect. Temperature-dependent values of the total electrical conductivity are reported, and the observed behavior appears distinctive from that of non-high entropy transition metal-based perovskites, beyond the expectations based on the rule-of-mixtures. In terms of formation of solid solutions in Sr-doped Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ materials, the results indicate a strong influence of the Ln radius, and while for La-based series the Sr solubility limit is at the level of xmax = 0.3, for the smaller Pr it is equal to just 0.1. In the case of Nd-, Sm- and Gd-based materials, even for the xSr = 0.1, the formation of secondary phases is observed on the SEM + EDS images.

2021 ◽  
Vol 57 (9) ◽  
pp. 919-928
Author(s):  
L. T. Denisova ◽  
M. S. Molokeev ◽  
Yu. F. Kargin ◽  
V. P. Gerasimov ◽  
A. S. Krylov ◽  
...  

2000 ◽  
Vol 15 (8) ◽  
pp. 1735-1741 ◽  
Author(s):  
Mojca Podlipnik ◽  
Danilo Suvorov ◽  
Matjaz Valant ◽  
Drago Kolar

Investigations of a substitutional mechanism of Pb incorporation into the crystal structure of Ba6−3xNd8+2xTi18O54 performed by x-ray diffraction analysis, scanning electron microscopy, and energy dispersive and wavelength dispersive x-ray spectroscopy revealed that Pb2+ substitutes for Ba2+ according to the formula (Ba1−zPbz)6−3xNd8+2xTi18O54. The solid solubility limit for 0.5 = x = 0.6 compositions was determined to be at 0.35 ≤ z < 0.4 (nominal composition) which, according to measurements of PbO loss occurring during the heat treatment, gives 0.30 ≤ z < 0.35 (analyses of matrix phase). Increasing the Pb2+ concentration in (Ba1−zPbz)4.5Nd9Ti18O54, results in tf decreasing from an initial positive value (80 ppm/K) to a negative value at the solid solubility limit (−25 ppm/K at z = 0.35). In the same concentration range the Q-value decreases from an initial 2000 to 1250 (z. = 0.35), measured at 4 GHz, while permittivity remains almost constant (k = 87 ± 1.5). After exceeding the solid solubility limit of Pb2+ in (Ba1−zPbz)4.5Nd9Ti18O54 the appearance of secondary phases (Nd4Ti9O24 and Pb-rich phase at grain boundaries) changes the trends of the microwave dielectric properties; permittivity decreases, Q-value remains almost constant, and Tf increases.


2021 ◽  
pp. 1-6
Author(s):  
Mariana M. V. M. Souza ◽  
Alex Maza ◽  
Pablo V. Tuza

In the present work, LaNi0.5Ti0.45Co0.05O3, LaNi0.45Co0.05Ti0.5O3, and LaNi0.5Ti0.5O3 perovskites were synthesized by the modified Pechini method. These materials were characterized using X-ray fluorescence, scanning electron microscopy, and powder X-ray diffraction coupled to the Rietveld method. The crystal structure of these materials is orthorhombic, with space group Pbnm (No 62). The unit-cell parameters are a = 5.535(5) Å, b = 5.527(3) Å, c = 7.819(7) Å, V = 239.2(3) Å3, for the LaNi0.5Ti0.45Co0.05O3, a = 5.538(6) Å, b = 5.528(4) Å, c = 7.825(10) Å, V = 239.5(4) Å3, for the LaNi0.45Co0.05Ti0.5O3, and a = 5.540(2) Å, b = 5.5334(15) Å, c = 7.834(3) Å, V = 240.2(1) Å3, for the LaNi0.5Ti0.5O3.


2016 ◽  
Vol 697 ◽  
pp. 327-330 ◽  
Author(s):  
Ke Shan ◽  
Xing Min Guo ◽  
Feng Rui Zhai ◽  
Zhong Zhou Yi

Y0.06Sr0.94Ti0.6Fe0.4O3-δ-YSZ composites were prepared by mixing Y, Fe co-doped SrTiO3 (Y0.06Sr0.94Ti0.6Fe0.4O3-δ known as YSTF) and 8 mol% Y2O3 stabilized ZrO2 (YSZ) in different weight fractions. The phase stability, phase compatibility, microstructure and mixed ionic-electronic conductivity of composites were investigated. Phase analysis by XRD showed no clearly detectable secondary phases. The electrical conductivity measurement on the YSTF-YSZ composites showed a drastic decrease in total electrical and ionic conductivities when more than 10 wt% of YSZ was used in the composites. The total electrical conductivity was 0.102 S/cm for Y0.06Sr0.94Ti0.6Fe0.4O3-δ and 0.043 S/cm for YSTF-20YSZ at 700 oC, respectively. The value at 700 oC is approximately 2.4 times higher than that of YSTF-20YSZ. The ionic conductivity of Y0.06Sr0.94Ti0.8Fe0.2O3-δ varies from 0.015S/cm at 700 oC to 0.02 S/cm at 800 oC, respectively. The value at 800°C is approximately 12.5 times higher than YSTF-20YSZ. The ion transference numbers of YSTF-YSZ composites vary from 0.14 to 0.28 at 800 °C.


2012 ◽  
Vol 196 ◽  
pp. 528-535 ◽  
Author(s):  
Sverre M. Selbach ◽  
Amund Nordli Løvik ◽  
Kristin Bergum ◽  
Julian R. Tolchard ◽  
Mari-Ann Einarsrud ◽  
...  

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