Densification, microwave dielectric properties and rattling effect of LiYbO2 ceramics with low εr and anomalous positive τf

LiYbO 2 ceramic with tetragonal structure formed only by [LiO 6 ] and [YbO 6 ] octahedra, exhibited a ε r of 13.3 ± 0.2, Q ×  f of 24,700 ± 500 GHz and an abnormal positive τ f of + 38.6 ± 3.0 ppm/°C as sintered at 1100 °C with low relative density of 88 %. Dense ceramic with relative density of 95.1 % was obtained with the addition of 1 wt% LiF when sintered at 1080 °C, exhibiting enhanced microwave dielectric properties of ε r = 14.3 ± 0.2, Q ×  f = 41,200 ± 500 GHz, τ f = +56.5 ± 3.0 ppm/°C and α L = 8.5 × 10 −6 /K. The large positive discrepancy as much as + 45.1 % between measured ε r with porosity correction and calculated ε r (C-M) using Clausius−Mossotti relations might be due to the rattling effect of Li + , which also led to the positive τ f .