Electronic structure, thermodynamic stability and high-temperature sensing properties of Er-α-SiAlON ceramics

Abstract

α-SiAlon ceramics have been in use as engineering ceramics in the most arduous industrial environments such as molten metal handling, cutting tools, gas turbine engines, extrusion molds, thermocouple sheaths, protective cover for high-temperature sensors, etc., owing to their outstanding mechanical, thermal and chemical stability. taking advantage of the intrinsic properties of α-SiAlons, we investigate, in this paper, the possibility of using the er-doped α-SiAlon (er-α-SiAlon) ceramic as a high-temperature sensing material via its unique near-infrared to visible upconversion property. We first use neutron diffraction and density functional theory calculations to study the electronic structure and thermodynamic stability of er-α-SiAlon. it is found that the interstitial doping of er stabilizes the α-SiAlON structure via chemical bonds with O-atoms with N:O ratio of 5:2 in the sevenfold coordination sites of the er 3+ ion. temperature-dependent upconversion emissions are then studied under 980 and 793 nm excitations over a temperature range of 298-1373 K and the fluorescence intensity ratio (fiR) technique has been employed to investigate the temperature sensing behavior. temperature-dependent Raman behavior is also investigated. We demonstrate that using er-α-SiAlon as a sensing material, the limit of temperature measurement via the fiR technique can be pushed well beyond 1200 K. SiAlON ceramics are high-performance refractory ceramics which are manufactured by combining raw materials silicon nitride, alumina, aluminum nitride along with the oxide of rare earth elements. The SiAlON ceramics exist in two basic forms; each form is isostructural with one of the two common forms of Si 3 N 4. In α-SiAlON, Si in the tetrahedral structure in Si 3 N 4 is replaced by Al with limited substitution of N by O. Valancy requirements are satisfied by modifying cations occupying the interstitial holes at (1/3, 2/3, z) and (2/3, 1/3, ½ + z) per unit cell of the α-Si 3 N 4 1. In this way cations of yttrium (Y), calcium (Ca), lithium (Li), neodymium (Nd), Erbium (Er), etc., for example, can be incorporated into the structure. Consequently, α-SiAlON has the general formula M x v+ Si 12−m−n Al m+n O n N 16−n where x = m/v and M is the metal cation 1. The interstitial dissolution of the M ion stabilizes the α-SiAlON structure and the cations M are coordinated by seven (N, O) atom sites 2,3. α-SiAlON ceramics are widely used for high-temperature and high-endurance applications owing to their ability to withstand high structural loads and their excellent thermal and chemical stability 4,5. Taking advantage of their superior mechanical, thermal and chemical stabilities, these materials have also been investigated recently for the possibility of functional applications such as downshifting phosphor materials for solid-state lighting 6. In another aspect of investigating the functional properties of these ceramics, we recently reported efficient near-infrared to visible frequency upconversion in lanthanides (Ln 3+)-doped α-SiAlON ceramics ...

Ceramic Cutting Materials and Tools Suitable for Machining High-Temperature Nickel-Based Alloys: A Review

“…x Si 12-m-n Al m+n O n N 16-n , where Li, Mg, Ca, Y, and/or a rare earth element refer to M, and by considering its ionic radius [138] or with using quenching. For entry of cations with considerable size in structure, the presence of other cations is required.…”

“…α-SiAlONs are isostructural with α-Si 3 N 4 in which chemical binding of m and n (Si-N) are substituted by Al-N (m) and Al-O (n) bonds, respectively, the schematic diagram of which is shown in Figure2[136][137][138]. In addition, supplementary cation for the stability of crystal lattice of α-SiAlONs is needed.…”

Ho-SiAlON Ceramics as Green Phosphors under Ultra-Violet Excitations

“…The N1s peak consists of three sub-peaks as shown in Figure 5 e. The weak sub-peak at the lowest binding energy corresponds to the N-Al, while the intense central peak corresponds to the N-Si bonds in the α-SiAlON lattice because the N1s binding energy for AlN is less than that for Si 3 N 4 [ 35 ]. In the α-SiAlON crystal, the Ln 3+ dopant (Ho 3+ ) occupies the seven-fold coordination site [ 5 , 21 ] for the charge compensation which arises due to the partial Al (Si)-O (N) substitution in the formation of the SiAlON lattice [ 3 ]. Hence, it is suggested that the broad sub-peak with the highest binding energy in Figure 5 e corresponds to the N-Ho bond.…”

“…On contrary, many other host materials, such as LaMgAl 11 O 19 [ 40 ], Y 2 O 3 [ 41 ], NaYF 4 [ 13 ], K 2 SiF 6 [ 12 ], etc., show a decrease in emission intensity due to concentration quenching at a high level of doping of the activators. An additional advantage of Ho-SiAlON ceramics as phosphors is that SiAlON ceramics have a very high laser damage threshold and high-temperature spectral stability [ 21 , 42 ] that make them suitable for high-power green emitting remote phosphors in extreme conditions [ 8 , 9 ].…”

“…α-Si 3 N 4 (UBE Co., Tokyo, Japan), AlN (Tokuyama Co., Tokyo, Japan), Al 2 O 3 , and Ho 2 O 3 (High purity chemicals Co LTD., Saitama, Japan) were used as starting materials. The samples were hot-press sintered at 1850 °C, as described elsewhere [ 20 , 21 ]. The samples were re-sized and polished for various characterizations.…”