## 3 Results  
### Mean Square Displacement  
The mean square displacement was obtained for all elements and glass compositions. The average _MSD_ for the selected glass composition and temperatures is presented in Figure 1. The curves exhibit similar behavior for all specific elements and compositions. Initially, there is a nonlinear rapid increase in the _MSD_. However, after a sufficiently long time (above, e.g., 200 ps), the trend becomes linear. For the linear part of the curve, the straight line was fitted as shown in Figure 1. The fitted slope of this line was used to evaluate a self-diffusion constant (\(D\)) based on Equation (1).  
The \(D\) parameters as a function of the inverse temperature for the specific elements of x = 30 glass are given in Figure 2.  
Figure 1: Exemplary average MSD as a function of time at the selected temperatures for x = 30 glass.  
It can be seen that the self-diffusion parameters increase rapidly with rising temperature. The lowest values are evidenced for the P atoms in the glass network sites and the intermediate Fe\({}^{\text{III}}\), which may occupy network or modifier positions in the glass. In contrast, the highest \(D\) values are associated with pure modifiers Sr and Fe\({}^{\text{II}}\).  
As an example, the average \(MSD\) for the exemplary x = 30 glass composition in the Arrhenius plot is shown in Figure 3. Similar curves are evidenced for all species and compositions. It can be noticed that there are three distinct regions of parameter slope change: the low-temperature region (1, represented by the blue line), the mid-temperature region (2, represented by the orange line), and the high-temperature region (3, represented by the green line) in Figure 3. In each of these regions, different self-diffusion activation energies (\(E\)) and pre-exponential factors (\(D_{i}\)) can be obtained using the following Arrhenius equation:  
\[D=D_{i}exp\left(\frac{-E}{k_{B}T}\right), \tag{3}\]  
where \(k_{B}\) is the Boltzmann constant.  
Figure 3: Arrhenius plot of the average self-diffusion coefficient for x = 30 glass (blue line—low-temperature region, orange line—mid-temperature region, green line—high-temperature).  
Figure 2: Calculated self-diffusion coefficients as a function of the reciprocal temperature for x = 30 glass.  
To the points in the regions, the lines were fitted and the fitted parameters were applied to determine the \(E\) and \(D_{i}\) parameters in each region. The lines intersect at low-temperature point T\({}_{1}\) and high-temperature point T\({}_{2}\), dividing the regions. The resulting parameter values for all species and glass compositions are summarized in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Composition** & **Parameter** & **Average** & **P** & **FeIII+** & **FeII** & **O** & **Sr** \\ \hline \multirow{6}{*}{x = 0} & T\({}_{1}\)/K & 958 & 971 & 990 & 963 & 951 & \\  & T\({}_{2}\)/K & 1942 & 1937 & 1864 & 1790 & 1989 & \\  & E\({}_{1}\)/eV & 0.082 & 0.075 & 0.086 & 0.090 & 0.081 & \\  & D\({}_{1}\)/10\({}^{-12}\) m\({}^{2}\)/s & 2.085 & 1.034 & 2.576 & 5.888 & 2.221 & \\  & E\({}_{2}\)/eV & 0.275 & 0.249 & 0.292 & 0.336 & 0.270 & \\  & D\({}_{2}\)/10\({}^{-11}\) m\({}^{2}\)/s & 2.178 & 0.822 & 2.903 & 1.139 & 2.207 & \\  & E\({}_{3}\)/eV & 1.839 & 2.037 & 1.859 & 1.716 & 1.823 & \\  & D The parameters summarized in Table 1 can be used to estimate self-diffusion coefficients at any desired temperature. The self-diffusion coefficients corresponding to the intermediate temperatures within the three regions are presented in Figure 4.