Microwave dielectric properties and crystal structure refinements in M (M=Sr, Ca) doped Nd2(Ba1–xMx)ZnO5 solid solutions

The microwave dielectric properties and crystal structure stability estimated by the bond valence sum of Nd2BaZnO5 (εr=22.6, τf=4.6 ppm/°C, Q·f =12,451 GHz), Nd2Ba0.5Sr0.5ZnO5 (εr=25.5, τf=26.0 ppm/°C, Q·f =6185 GHz) and Nd2Ba0.5Ca0.5ZnO5 (εr=26.4, τf=24.0 ppm/°C, Q·f =6210 GHz) were evaluated in this study. It was clarified that substituting Sr or Ca for Ba induces the decrease of lattice parameters at Nd2Ba0.5Sr0.5ZnO5 (a=6.7391(4), c=11.4592(4) ) and Nd2Ba0.5Ca0.5ZnO5 (a=6.7386(4), c=11.4597(5) ) in comparison with those of Nd2BaZnO5 ( a=6.7391(4), c=11.4592(4) ) and volume of BaO10 polyhedron by Rietveld analysis. In this case, an instability in the crystal structure of Nd2Ba0.5Sr0.5ZnO5 and Nd2Ba0.5Ca0.5ZnO5 is induced by the bond valence difference between Ba and Sr or Ca ions. Our research that the crystal structure instability in particular influences a decrease of the Q·f value in this system.