Conductivity spectrum and relaxations in mixed alkali fluorophosphate glasses

摘要

Ionic conductivity and electrical relaxations in fast ion conducting glasses (also known as 'ion dynamics') is usually investigated from electrical condcutivity relaxations, represented by the ac conductivity from near zero frequency (dc) to the far or mid infrared spectrum, to which relaxations of the ion and network motions contribute. I nthe present work ion dynamics of LiF-KF-Al(PO_3)_3 glasses is reported. Glasses in this system have been synthesised via conventional melt-quench route. The glass-transition temeprautre (T_g), dc conductivity and electrical relaxations were studied. The conductivity spectrum of the 0.8 LiF-0.2Al(PO_3)_3 glass was recorded at rom temperature covering 17 decades in frequency. A binary composition was investigated over a broad band of frequency from 1mHz to 150 THz employing various techniques. A complete conductivity spectrum was constructed by combining the impedance measurements at low frequencies and the dielectric data obtained at high freuqencies. A maximum conductivity of 38 ( omega ~-1 cm~-1) at 3.4 x 10~13 Hz agreed with the theoretically predicted value. For mixed cation glasses, the frequency dependent ocnductivity was measured in the frequency range 20 Hz to 2 GHz and at temperatures 100 K <= T <= 523 K. While the dc conductivity showed a characteristic minimum with composition, the ac conductivity also exhibited the mixed alkali effect. This is the first experimental boservation and will be discussed.