Study of structural and optical properties of the thermochromic silver and copper tetraiodomercurates (Ag 2 , Cu 2 ) HgI
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Study of structural and optical properties of the thermochromic silver and copper tetraiodomercurates (Ag2, Cu2) HgI4 ceramics Misael Chocolatl‑Torres1 · Adriana Paola Franco‑Bacca2 · Jorge Andrés Ramírez‑Rincón2 · Cindy Lorena Gómez‑Heredia2 · Fernando Cervantes‑Alvarez2 · Juan José Alvarado‑Gil2 · Rutilo Silva‑Gonzalez1 · Miller Toledo3 · Ulises Salazar‑Kuri1 Received: 6 February 2020 / Accepted: 2 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Powders of silver (Ag2HgI4) and copper (Cu2HgI4) tetraiodomercurates were synthesized by a simple co-precipitation method. Their phase transition behavior was investigated by differential scanning calorimetry, X-ray diffraction (XRD), as well as diffuse reflectance to determine its reversibility and stability during heating–cooling cycles. Calorimetry showed a sharp u2HgI4 samples in the first cycle, one transition at 51 °C when heating, and at 40 °C when cooling for A g2HgI4 samples. For C peak was observed when heating at 69.6 and 49.7 °C when cooling. However, in these samples, the first peak splits into two peaks when heating during the second and third cycles (67.5 and 57.8 °C), indicating a probable loss of crystallinity. XRD and diffuse reflectance showed that the transition starts almost since the beginning of the warming-up process and is more evident around 40 °C for Ag2HgI4 and around 60 °C for Cu2HgI4. The energy bandgap indicates that Ag2HgI4 and C u2HgI4 behave differently during the transition. Copper tetraiodomercurate follows almost the same path for heating than for cooling. Its reversible thermochromic and superionic properties are promising for several applications and open the possibility of using them as inclusions in smart composite systems. Keywords Thermochromic · Reflectivity · Heat capacity · Thermodiffraction
1 Introduction Chromogenic materials change color when subjected to external influence or stimulus, the most studied are the thermochromic, photochromic and electrochromic materials, in which the applied stimulus are: heating, light irradiation, and electric field, respectively [1]. One of the most * Fernando Cervantes‑Alvarez [email protected] * Ulises Salazar‑Kuri [email protected] 1
Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apdo. Postal J‑48, 72570 Puebla, Mexico
2
Departamento de Física Aplicada, Centro de Investigación y de Estudios Avanzados del IPN, Carretera antigua a Progreso km 6, 97310 Mérida, Yucatán, Mexico
3
Facultad de Ciencias Físico‑Matemáticas, CONACYT-Benemérita Universidad Autónoma de Puebla, Av. San Claudio y Av. 18 sur, Col. San Manuel Ciudad Universitaria, C. P. 72570 Puebla, Mexico
common applications of chromogenic materials is in energy saving using them in the built environment, also offering an indoor comfort increase for the building users [2]. In particular thermochromic materials are those which change their refractive index upon reaching a characteristic transition temperature. This change can be revers
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