Low temperature ultrasonic attenuation in phosphate glasses

Ultrasonic attenuation measurements on phosphate glasses with different chain lengths, lead metaphosphate and lead-indium phosphate, have been carried out at low temperatures (0.3 10 K) and high frequencies (100 160 MHz). The materials investigated are lead metaphosphate (average chain length > 15) and lead indium phosphate (average chain length = 3). Both materials have the typical glasslike behavior, explained by the presence of tunneling states (TS). A detailed analysis reveals that the density of states of these TS is significantly lower in the lead metaphosphate glass compared to the lead indium glass. This difference can be related to the difference in length of the phosphate tetrahedra chains.