Considering that the refractive index of glass (SLS) depends on density and polarizability.
1- Which of these two factors has a greater effect on the refractive index?
2- Which of the compounds of iron oxide and titanium oxide has a greater effect on the refractive index of glass?
3- What is the effect of adding alkaline and alkaline earth oxides?
Please introduce if you know a complete source in this regard.
Davood Ghanei Thank you for your interesting question and one I have spent some time working on during my career. A good starting point is the paper I wrote for WCPT7 and attached. This contains some pertinent references although the Brainshark url’s no longer function. A series of general webinars on optical properties (free registration required) makes reference to this paper and others. For your question the second one in the series may be more relevant:
- Laser Diffraction Masterclass: Why do you Need Material Optical Properties?
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W200211LDBasics1.html
- Laser Diffraction Masterclass 2: How Can Material Optical Properties be Calculated/Estimated
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W200317LDBasics2.html
- Laser Diffraction Masterclass 3: Optical Properties - How Can Material Optical Properties be Measured
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W200414OpticalProp.html
To answer your specific questions:
1- Which of these two factors (density, polarizability) has a greater effect on the refractive index?
The refractive index of silica and soda lime glass (plus additives) is directly related to the measured density. This is inferred by the Gladstone-Dale relationship (in this case, approximately RI = 0.195ρ + 1.03). See attached slide with a reference to Pulker. The molar electronic polarizability per oxide atom is directly and inherently linked to the refractive index via the Clausius-Mossotti/Lorentz-Lorenz term (n2 – 1)/(n2 +2) so it’s a bit strange to ask about a relationship between RI and polarizability
2- Which of the compounds of iron oxide and titanium oxide has a greater effect on the refractive index of glass?
As we increase the proportions of any oxide additive to soda lime glass then the RI will increase (and the density generally, as silica/soda lime glass isn’t particularly dense to begin with). The greater the RI of the additive than the greater the resultant RI. However, there are a number of forms of iron oxide (e.g. magnetite, hematite) and titania (rutile, anatase, brookite) all with differing (and in some cases, overlapping) optical properties. You do not state which oxide form/compound you are referring to. The highly birefringent nature of the TiO2 morphs will also play a significant role. The biggest effect of iron oxide (in any form) is likely to (dis)color the glass to brown. This is likely a deleterious effect unless it’s required (e.g. for beer or wine bottles). The RI’s of a number of these compounds at 632.8 nm can be found by a simple on-line search:
Magnetite: 2.36 https://refractiveindex.info/?shelf=main&book=Fe3O4&page=Querry
Hematite 3.13 https://refractiveindex.info/?shelf=main&book=Fe2O3&page=Querry-o
TiO2: A good general reference is Dana but I also attach a paper entitled 'Effect of TiO2 on optical properties of glasses in the soda-lime-silicate system'. At 632.8 nm the average of the extraordinary and ordinary rays is the following (see second webinar above with the measured densities and a Gladstone-Dale calculation): rutile (2.755), anatase (2.525), and brookite (2.652). Thus you’ll note that magnetite has the highest RI of all the iron oxides but hematite has a lower RI.
3- What is the effect of adding alkaline and alkaline earth oxides?
See the answers to 1. and 2. above
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