Structural and transport properties of A2HoTaO6 [A=Ba, Sr, and Ca]

Double perovskite oxides A2HoTaO6 [A=Ba, Sr, and Ca] are synthesized by a solid state reaction technique. The Rietveld refinement of the X-ray diffraction pattern shows that Ba2HoTaO6 crystalizes in cubic Fm3m symmetry whereas Sr2HoTaO6 and Ca2HoTaO6 adopt the monoclinic P21/n symmetry. The field cooled and zero field cooled magnetic susceptibilities of the materials are measured in the temperature range from 5 K to 300 K. The temperature dependence of inverse magnetic susceptibility shows the antiferromagnetic behavior of these systems. The dielectric relaxation of the samples is investigated by the Cole–Cole model in the frequency range from 50 Hz to 1 MHz and in the temperature range from 303 K to 673 K. The frequency dependent conductivity spectra follow the power law. The scaling behavior of the imaginary part of the impedance spectra suggests that the relaxation shows the same mechanism at various temperatures. - Highlights: • The Rietveld refinement indicates that B2HoTaO6 has cubic Fm3m symmetry. • Sr2HoTaO6 and Ca2HoTaO6 adopt the monoclinic P21/n crystal symmetry. • The temperature dependence of inverse magnetic susceptibilities follows the Curie–Wiess law. • The superexchange interaction between the Ho ions leads to antiferromagnetism in these systems. • Dielectric relaxation mechanism is explained using the Cole–Cole model