The ideal temperature for achieving perfectly crystalline SnO2 can vary depending on the specific synthesis method and desired crystal size. However, research suggests that temperatures in the range of 400°C to 600°C are commonly used to obtain well-crystallized SnO2.

Here are some key factors to consider:

• Synthesis Method: Different synthesis methods have different optimal temperature ranges. For example, sol-gel methods often require lower temperatures (around 400°C) for crystallization, while hydrothermal methods may require higher temperatures (around 600°C).
• Desired Crystal Size: Smaller crystal sizes may require lower temperatures to prevent excessive growth, while larger crystals may benefit from higher temperatures to promote crystallization.
• Annealing Time: The duration of annealing at the chosen temperature also plays a crucial role in achieving crystallinity. Longer annealing times can improve crystal quality.

1) Since u haven't doped try annealing around 450-550 °C for 2-4 hrs. Annealing comes with risk... If u r expecting crystalite size to be