my suggestion is as below which can be wrong but might be helpful

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The formation of different phases in zirconium oxide (ZrO2​), also known as zirconia, is a fundamental characteristic of the material that is both a challenge and a powerful tool in materials engineering. While your question asks about two “phrases” (which we’ll interpret as phases), pure zirconia actually has three distinct solid phases. The reason we often talk about two phases coexisting is due to a process called stabilization, which is done to create high-performance ceramics.

Let’s break down the reason in detail, from the fundamental science to the engineering application.

1. The Three Natural Phases of Pure Zirconia

At its core, the reason zirconium oxide forms different phases is due to thermodynamics. Like many materials, its atoms arrange themselves into the most energetically stable crystal structure for a given temperature and pressure. As the temperature changes, the stable structure can change.

For pure zirconium oxide (ZrO2​), these are the three temperature-dependent phases:

2. The Problem: The Destructive Phase Transformation

If you make a part out of pure zirconia by sintering it at a high temperature (e.g., 1500 °C, where it is in the tetragonal phase) and then cool it down, a catastrophic event happens.

As the material cools below 1170 °C, it tries to transform from the tetragonal phase back to the monoclinic phase. This transformation is not subtle; it is accompanied by a significant volume expansion of about 3% to 5%.

This sudden expansion creates immense internal stresses within the material. The stresses are so large that the material cannot withstand them, leading to severe cracking and the complete disintegration of the ceramic part. This makes pure zirconia almost useless for any application that requires cooling from a high processing temperature.

3. The Solution: Stabilization (Creating Two-Phase Systems)

This is where your question about “two phases” becomes highly relevant. To prevent this self-destruction, materials scientists add other oxides, called stabilizers or dopants, into the zirconia crystal lattice. Common stabilizers include:

• Yttrium Oxide (Y2O3​) - Most common
• Calcium Oxide (CaO)
• Magnesium Oxide (Mg)
• Cerium(III) Oxide (Ce2O3​)

These dopant atoms substitute for some of the zirconium atoms in the crystal lattice and energetically favor the higher-symmetry tetragonal or cubic phases, effectively “tricking” them into remaining stable (or metastable) even at room temperature.

This leads to several types of “stabilized zirconia,” which often consist of two phases:

• Partially Stabilized Zirconia (PSZ): In this type, enough stabilizer is added (e.g., 8 mol% MgO) to form a matrix of the cubic phase, with fine precipitates of the tetragonal phase dispersed within it. Here, you have two phases—cubic and tetragonal—coexisting at room temperature.
• Tetragonal Zirconia Polycrystal (TZP): This is the most common high-strength zirconia. A smaller amount of stabilizer is added (e.g., 3 mol% Yttria, known as 3Y-TZP). This is just enough to keep the entire material in the tetragonal phase at room temperature. This phase is “metastable,” meaning it’s not the most energetically stable state (monoclinic is), but it’s trapped in the tetragonal form and won’t transform without a trigger.

4. The Main Reason: Transformation Toughening

Why go through all this trouble to create a material with a metastable tetragonal phase? The reason is a remarkable mechanism called transformation toughening, which gives zirconia its famous strength and fracture resistance, earning it the name “ceramic steel.”

Here’s how it works:

This ability to self-heal and arrest cracks is the primary reason why stabilized zirconia is one of the toughest ceramic materials available.

I don't understand your question. Have you obtained two phases in your synthesized sample? Zirconia is an oxide that presents polymorphism, having three crystal forms stable at different temperatures. You can stabilize one of them also at ambient temperature by adding for example small amount of other oxides, obtaining the so called partially stabilized zirconia.

If you can better explain your request maybe we can help you