Mandanici A, Raimondo A, Cutroni M, Ramos M A, Rodrigo J G, Vieira S, Armellini C, Rocca F
Dipartimento di Fisica, Università di Messina, Salita Sperone 31, 98100 Messina, Italy.
J Chem Phys. 2009 May 28;130(20):204508. doi: 10.1063/1.3139450.
Ionic glasses obtained combining silver iodide and silver molybdate are characterized by quite low values of the glass transition temperature T(g) around 320-350 K, by high values of the dc ionic conductivity even at room temperature and by a peculiar behavior of the mechanical response at ultrasonic frequencies. In fact, at temperatures well below their glass transition temperature, these glasses exhibit an intense peak of acoustic attenuation well described by two different and almost overlapping relaxational contributions. Considering also that negative thermal expansion has been reported for some molybdate crystalline compounds, we have investigated in this work the thermal expansion of two silver iodomolybdate glasses (AgI)(1-x)(Ag(2)MoO(4))(x) for x=0.25 and x=0.33 in a wide temperature range (4.2-300 K) from cryogenic temperatures up to some 20 K below T(g) using a precision capacitance dilatometer aiming to understand whether the expansivity shows some possible fingerprint corresponding to the above-mentioned mechanical response. Two different measuring methods, a quasiadiabatic and a continuous one, have been used for the thermal expansion measurements. The results are discussed in comparison with the information obtained from previous investigations based on the extended x-ray absorption fine structure (EXAFS) technique and with the behavior of other ionic glasses.
玻璃化转变温度T(g)相当低，约为320 - 350K；即使在室温下直流离子电导率也很高；在超声频率下具有独特的机械响应行为。事实上，在远低于其玻璃化转变温度的温度下，这些玻璃表现出一个强烈的声衰减峰，该峰可以由两种不同且几乎重叠的弛豫贡献很好地描述。考虑到一些钼酸盐晶体化合物已被报道具有负热膨胀，我们在这项工作中使用精密电容膨胀仪研究了两种碘钼酸银玻璃(AgI)(1 - x)(Ag₂MoO₄)(x)（x = 0.25和x = 0.33）在从低温温度到比T(g)低约20K的宽温度范围（4.2 - 300K）内的热膨胀，旨在了解膨胀系数是否显示出与上述机械响应相对应的一些可能特征。热膨胀测量使用了两种不同的测量方法，一种是准绝热法，另一种是连续法。将结果与基于扩展X射线吸收精细结构（EXAFS）技术的先前研究获得的信息以及其他离子玻璃的行为进行了比较讨论。
