diff --git a/docs/source/tutorials/python/phonons.ipynb b/docs/source/tutorials/python/phonons.ipynb
index dd9bdd28..96e7a49c 100644
--- a/docs/source/tutorials/python/phonons.ipynb
+++ b/docs/source/tutorials/python/phonons.ipynb
@@ -140,7 +140,7 @@
     "    temp_min=0.0,\n",
     "    temp_max=1000.0,\n",
     "    minimize=False,\n",
-    "    force_consts_to_hdf5=True,\n",
+    "    hdf5=True,\n",
     "    plot_to_file=True,\n",
     "    symmetrize=False,\n",
     "    write_full=True,\n",
@@ -249,7 +249,7 @@
     "    temp_min=0.0,\n",
     "    temp_max=1000.0,\n",
     "    minimize=True,\n",
-    "    force_consts_to_hdf5=True,\n",
+    "    hdf5=True,\n",
     "    plot_to_file=True,\n",
     "    symmetrize=False,\n",
     "    write_full=True,\n",
@@ -317,7 +317,7 @@
     "    temp_min=0.0,\n",
     "    temp_max=1000.0,\n",
     "    minimize=True,\n",
-    "    force_consts_to_hdf5=True,\n",
+    "    hdf5=True,\n",
     "    plot_to_file=True,\n",
     "    symmetrize=False,\n",
     "    write_full=True,\n",
@@ -399,7 +399,7 @@
     "    temp_min=0.0,\n",
     "    temp_max=1000.0,\n",
     "    minimize=True,\n",
-    "    force_consts_to_hdf5=True,\n",
+    "    hdf5=True,\n",
     "    plot_to_file=True,\n",
     "    symmetrize=False,\n",
     "    write_full=True,\n",
@@ -440,7 +440,7 @@
     "    temp_min=0.0,\n",
     "    temp_max=1000.0,\n",
     "    minimize=True,\n",
-    "    force_consts_to_hdf5=True,\n",
+    "    hdf5=True,\n",
     "    plot_to_file=True,\n",
     "    symmetrize=False,\n",
     "    write_full=True,\n",
diff --git a/docs/source/user_guide/command_line.rst b/docs/source/user_guide/command_line.rst
index 21641135..2644d166 100644
--- a/docs/source/user_guide/command_line.rst
+++ b/docs/source/user_guide/command_line.rst
@@ -494,7 +494,7 @@ This will save the Phonopy parameters, including displacements and force constan
 in addition to generating a log file, ``NaCl-phonons-log.yml``, and summary of inputs, ``NaCl-phonons-summary.yml``.
 
 Additionally, the ``--bands`` option can be added to calculate the band structure
-and save the results to a compressed yaml file, ``NaCl-auto_bands.yml.xz``:
+and save the results to a compressed yaml file, ``NaCl-auto_bands.hdf5``:
 
 .. code-block:: bash
 
@@ -533,7 +533,7 @@ but band paths can also be specified explicitly using the ``--paths`` option to
     janus phonons --struct tests/data/NaCl.cif --arch mace_mp --bands --plot-to-file --paths tests/data/paths.yml
 
 
-This will save the results in a compressed yaml file, ``NaCl-bands.yml.xz``, as well as the generated plot, ``NaCl-bands.svg``.
+This will save the results in a compressed yaml file, ``NaCl-bands.hdf5``, as well as the generated plot, ``NaCl-bands.svg``.
 
 The ``--paths`` file must include:
 
diff --git a/janus_core/calculations/phonons.py b/janus_core/calculations/phonons.py
index ae7e079c..5c4c3369 100644
--- a/janus_core/calculations/phonons.py
+++ b/janus_core/calculations/phonons.py
@@ -4,6 +4,7 @@
 
 from collections.abc import Sequence
 from typing import Any, get_args
+from warnings import warn
 
 from ase import Atoms
 from numpy import ndarray
@@ -108,7 +109,9 @@ class Phonons(BaseCalculation):
     temp_step
         Temperature step for thermal properties calculations, in K. Default is 50.0.
     force_consts_to_hdf5
-        Whether to write force constants in hdf format or not. Default is True.
+        Deprecated. Please use `hdf5`.
+    hdf5
+        Whether to write force constants and bands in hdf5 or not. Default is True.
     plot_to_file
         Whether to plot various graphs as band stuctures, dos/pdos in svg.
         Default is False.
@@ -159,7 +162,8 @@ def __init__(
         temp_min: float = 0.0,
         temp_max: float = 1000.0,
         temp_step: float = 50.0,
-        force_consts_to_hdf5: bool = True,
+        force_consts_to_hdf5: bool | None = None,
+        hdf5: bool = True,
         plot_to_file: bool = False,
         write_results: bool = True,
         write_full: bool = True,
@@ -238,7 +242,9 @@ def __init__(
         temp_step
             Temperature step for thermal calculations, in K. Default is 50.0.
         force_consts_to_hdf5
-            Whether to write force constants in hdf format or not. Default is True.
+            Deprecated. Please use `hdf5`.
+        hdf5
+            Whether to write force constants and bands in hdf5 or not. Default is True.
         plot_to_file
             Whether to plot various graphs as band stuctures, dos/pdos in svg.
             Default is False.
@@ -277,12 +283,27 @@ def __init__(
         self.temp_min = temp_min
         self.temp_max = temp_max
         self.temp_step = temp_step
-        self.force_consts_to_hdf5 = force_consts_to_hdf5
+        self.hdf5 = hdf5
         self.plot_to_file = plot_to_file
         self.write_results = write_results
         self.write_full = write_full
         self.enable_progress_bar = enable_progress_bar
 
+        # Handle deprecation
+        if force_consts_to_hdf5 is not None:
+            if hdf5 is False:
+                raise ValueError(
+                    """`force_consts_to_hdf5`: has replaced `hdf5`.
+                     Please only use `hdf5`"""
+                )
+            self.hdf5 = force_consts_to_hdf5
+            warn(
+                """`force_consts_to_hdf5` has been deprecated.
+                Please use `hdf5`.""",
+                FutureWarning,
+                stacklevel=2,
+            )
+
         # Ensure supercell is a valid list
         self.supercell = [supercell] * 3 if isinstance(supercell, int) else supercell
         if len(self.supercell) not in [3, 9]:
@@ -340,10 +361,11 @@ def __init__(
         # Output files
         self.phonopy_file = self._build_filename("phonopy.yml")
         self.force_consts_file = self._build_filename("force_constants.hdf5")
-        if self.qpoint_file:
-            self.bands_file = self._build_filename("bands.yml.xz")
-        else:
-            self.bands_file = self._build_filename("auto_bands.yml.xz")
+
+        filename = "bands" + (".hdf5" if hdf5 else ".yml")
+        if not self.qpoint_file:
+            filename = f"auto_{filename}"
+        self.bands_file = self._build_filename(filename)
         self.bands_plot_file = self._build_filename("bands.svg")
         self.dos_file = self._build_filename("dos.dat")
         self.dos_plot_file = self._build_filename("dos.svg")
@@ -430,9 +452,7 @@ def output_files(self) -> None:
         return {
             "log": self.log_kwargs["filename"] if self.logger else None,
             "params": self.phonopy_file if self.write_results else None,
-            "force_constants": (
-                self.force_consts_file if self.force_consts_to_hdf5 else None
-            ),
+            "force_constants": (self.force_consts_file if self.hdf5 else None),
             "bands": (
                 self.bands_file
                 if self.write_results and "bands" in self.calcs
@@ -552,7 +572,7 @@ def write_force_constants(
         self,
         *,
         phonopy_file: PathLike | None = None,
-        force_consts_to_hdf5: bool | None = None,
+        hdf5: bool | None = None,
         force_consts_file: PathLike | None = None,
     ) -> None:
         """
@@ -563,11 +583,11 @@ def write_force_constants(
         phonopy_file
             Name of yaml file to save params of phonopy and optionally force constants.
             Default is inferred from `file_prefix`.
-        force_consts_to_hdf5
+        hdf5
             Whether to save the force constants separately to an hdf5 file. Default is
-            self.force_consts_to_hdf5.
+            self.hdf5.
         force_consts_file
-            Name of hdf5 file to save force constants. Unused if `force_consts_to_hdf5`
+            Name of hdf5 file to save force constants. Unused if `hdf5`
             is False. Default is inferred from `file_prefix`.
         """
         if "phonon" not in self.results:
@@ -576,8 +596,8 @@ def write_force_constants(
                 "Please run `calc_force_constants` first"
             )
 
-        if force_consts_to_hdf5 is None:
-            force_consts_to_hdf5 = self.force_consts_to_hdf5
+        if hdf5 is None:
+            hdf5 = self.hdf5
 
         if phonopy_file:
             self.phonopy_file = phonopy_file
@@ -586,11 +606,11 @@ def write_force_constants(
 
         phonon = self.results["phonon"]
 
-        save_force_consts = not force_consts_to_hdf5
+        save_force_consts = not hdf5
         build_file_dir(self.phonopy_file)
         phonon.save(self.phonopy_file, settings={"force_constants": save_force_consts})
 
-        if force_consts_to_hdf5:
+        if hdf5:
             build_file_dir(self.force_consts_file)
             write_force_constants_to_hdf5(
                 phonon.force_constants, filename=self.force_consts_file
@@ -621,6 +641,7 @@ def calc_bands(self, write_bands: bool | None = None, **kwargs) -> None:
     def write_bands(
         self,
         *,
+        hdf5: bool | None = None,
         bands_file: PathLike | None = None,
         save_plots: bool | None = None,
         plot_file: PathLike | None = None,
@@ -630,6 +651,9 @@ def write_bands(
 
         Parameters
         ----------
+        hdf5
+            Whether to save the bands in an hdf5 file. Default is
+            self.hdf5.
         bands_file
             Name of yaml file to save band structure. Default is inferred from
             `file_prefix`.
@@ -645,11 +669,15 @@ def write_bands(
                 "Please run `calc_force_constants` first"
             )
 
+        if hdf5 is None:
+            hdf5 = self.hdf5
+
         if save_plots is None:
             save_plots = self.plot_to_file
 
         if bands_file:
             self.bands_file = bands_file
+
         if plot_file:
             self.bands_plot_file = plot_file
 
@@ -682,10 +710,14 @@ def write_bands(
         )
 
         build_file_dir(self.bands_file)
-        self.results["phonon"].write_yaml_band_structure(
-            filename=self.bands_file,
-            compression="lzma",
-        )
+        if hdf5:
+            self.results["phonon"].write_hdf5_band_structure(
+                filename=self.bands_file,
+            )
+        else:
+            self.results["phonon"].write_yaml_band_structure(
+                filename=self.bands_file,
+            )
 
         bplt = self.results["phonon"].plot_band_structure()
         if save_plots:
diff --git a/janus_core/cli/phonons.py b/janus_core/cli/phonons.py
index 24786521..504f8c2f 100644
--- a/janus_core/cli/phonons.py
+++ b/janus_core/cli/phonons.py
@@ -26,7 +26,7 @@
     Summary,
     Tracker,
 )
-from janus_core.cli.utils import yaml_converter_callback
+from janus_core.cli.utils import deprecated_option, yaml_converter_callback
 
 app = Typer()
 
@@ -110,11 +110,20 @@ def phonons(
         ),
     ] = 0.1,
     minimize_kwargs: MinimizeKwargs = None,
-    hdf5: Annotated[
+    force_consts_to_hdf5: Annotated[
         bool,
         Option(
             help="Whether to save force constants in hdf5.",
             rich_help_panel="Calculation",
+            callback=deprecated_option,
+            hidden=True,
+        ),
+    ] = None,
+    hdf5: Annotated[
+        bool,
+        Option(
+            help="Whether to save force constants and bands in hdf5.",
+            rich_help_panel="Calculation",
         ),
     ] = True,
     plot_to_file: Annotated[
@@ -228,8 +237,11 @@ def phonons(
         Default is 0.1.
     minimize_kwargs
         Other keyword arguments to pass to geometry optimizer. Default is {}.
+    force_consts_to_hdf5
+        Deprecated. Please use `hdf5`.
     hdf5
-        Whether to save force constants in hdf5 format. Default is True.
+        Whether to save force constants and bands in hdf5 format.
+        Default is True.
     plot_to_file
         Whether to plot. Default is False.
     write_full
@@ -391,7 +403,7 @@ def phonons(
         "temp_min": temp_min,
         "temp_max": temp_max,
         "temp_step": temp_step,
-        "force_consts_to_hdf5": hdf5,
+        "hdf5": hdf5,
         "plot_to_file": plot_to_file,
         "write_results": True,
         "write_full": write_full,
diff --git a/pyproject.toml b/pyproject.toml
index 15a41715..7f2a2940 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -30,7 +30,7 @@ dependencies = [
     "click<9,>=8.2.1",
     "codecarbon<4.0.0,>=3.0.4",
     "numpy<3.0.0,>=1.26.4",
-    "phonopy<3.0.0,>=2.23.1",
+    "phonopy<3.0.0,>=2.39.0",
     "pymatgen>=2025.1.24",
     "pyyaml<7.0.0,>=6.0.1",
     "rich<14.0.0,>=13.9.1",
diff --git a/tests/test_phonons.py b/tests/test_phonons.py
index 4706d3b8..f4e8df28 100644
--- a/tests/test_phonons.py
+++ b/tests/test_phonons.py
@@ -40,6 +40,22 @@ def test_calc_phonons():
     assert "phonon" in phonons.results
 
 
+def test_force_consts_to_hdf5_deprecation():
+    """Test deprecation of force-consts-to-hdf5."""
+    struct = read(DATA_PATH / "NaCl.cif")
+    struct.calc = choose_calculator(arch="mace_mp", model=MODEL_PATH)
+    with pytest.warns(
+        FutureWarning, match="`force_consts_to_hdf5` has been deprecated."
+    ):
+        phonons = Phonons(
+            struct=struct,
+            force_consts_to_hdf5=True,
+        )
+
+    phonons.calc_force_constants(write_force_consts=True)
+    assert "phonon" in phonons.results
+
+
 def test_optimize(tmp_path):
     """Test optimizing structure before calculation."""
     log_file = tmp_path / "phonons.log"
diff --git a/tests/test_phonons_cli.py b/tests/test_phonons_cli.py
index 19d03acf..7ee9b85b 100644
--- a/tests/test_phonons_cli.py
+++ b/tests/test_phonons_cli.py
@@ -2,10 +2,10 @@
 
 from __future__ import annotations
 
-import lzma
 from pathlib import Path
 
 from ase.io import read
+from h5py import File as HDF5Open
 import pytest
 from typer.testing import CliRunner
 import yaml
@@ -37,7 +37,7 @@ def test_phonons(tmp_path):
     with chdir(tmp_path):
         results_dir = Path("janus_results")
         phonopy_path = results_dir / "NaCl-phonopy.yml"
-        bands_path = results_dir / "NaCl-auto_bands.yml.xz"
+        bands_path = results_dir / "NaCl-auto_bands.yml"
         log_path = results_dir / "NaCl-phonons-log.yml"
         summary_path = results_dir / "NaCl-phonons-summary.yml"
 
@@ -66,14 +66,12 @@ def test_phonons(tmp_path):
 
         has_eigenvectors = False
         has_velocity = False
-        with lzma.open(bands_path, mode="rt") as file:
-            for line in file:
-                if "eigenvector" in line:
-                    has_eigenvectors = True
-                if "group_velocity" in line:
-                    has_velocity = True
-                if has_eigenvectors and has_velocity:
-                    break
+        with open(bands_path, encoding="utf8") as file:
+            bands = yaml.safe_load(file)
+            if "eigenvector" in bands["phonon"][0]["band"][0]:
+                has_eigenvectors = True
+            if "group_velocity" in bands["phonon"][0]["band"][0]:
+                has_velocity = True
         assert has_eigenvectors and has_velocity
 
         assert "command" in phonon_summary
@@ -109,7 +107,7 @@ def test_phonons(tmp_path):
 def test_bands_simple(tmp_path):
     """Test calculating force constants and reduced bands information."""
     file_prefix = tmp_path / "NaCl"
-    autoband_results = tmp_path / "NaCl-auto_bands.yml.xz"
+    autoband_results = tmp_path / "NaCl-auto_bands.yml"
     summary_path = tmp_path / "NaCl-phonons-summary.yml"
 
     result = runner.invoke(
@@ -132,7 +130,7 @@ def test_bands_simple(tmp_path):
     assert result.exit_code == 0
 
     assert autoband_results.exists()
-    with lzma.open(autoband_results, mode="rb") as file:
+    with open(autoband_results, encoding="utf-8") as file:
         bands = yaml.safe_load(file)
     assert "eigenvector" not in bands["phonon"][0]["band"][0]
     assert bands["nqpoint"] == 126
@@ -149,10 +147,11 @@ def test_bands_simple(tmp_path):
 
 
 def test_hdf5(tmp_path):
-    """Test saving force constants to HDF5 in new directory."""
+    """Test saving force constants and bands to HDF5 in new directory."""
     file_prefix = tmp_path / "test" / "NaCl"
     phonon_results = tmp_path / "test" / "NaCl-phonopy.yml"
     hdf5_results = tmp_path / "test" / "NaCl-force_constants.hdf5"
+    bands_results = tmp_path / "test" / "NaCl-auto_bands.hdf5"
     summary_path = tmp_path / "test" / "NaCl-phonons-summary.yml"
     log_path = tmp_path / "test" / "NaCl-phonons-log.yml"
 
@@ -164,6 +163,7 @@ def test_hdf5(tmp_path):
             DATA_PATH / "NaCl.cif",
             "--arch",
             "mace_mp",
+            "--bands",
             "--file-prefix",
             file_prefix,
             "--hdf5",
@@ -172,6 +172,69 @@ def test_hdf5(tmp_path):
     assert result.exit_code == 0
     assert phonon_results.exists()
     assert hdf5_results.exists()
+    assert bands_results.exists()
+
+    # Read phonons summary file
+    with open(summary_path, encoding="utf8") as file:
+        phonon_summary = yaml.safe_load(file)
+
+    output_files = {
+        "params": phonon_results,
+        "force_constants": hdf5_results,
+        "bands": bands_results,
+        "bands_plot": None,
+        "dos": None,
+        "dos_plot": None,
+        "band_dos_plot": None,
+        "pdos": None,
+        "pdos_plot": None,
+        "thermal": None,
+        "minimized_initial_structure": None,
+        "log": log_path,
+        "summary": summary_path,
+    }
+    check_output_files(summary=phonon_summary, output_files=output_files)
+    has_eigenvectors = False
+    has_velocity = False
+    nqpoints = 0
+    with HDF5Open(bands_results, "r") as bands:
+        if "eigenvector" in bands:
+            has_eigenvectors = True
+        if "group_velocity" in bands:
+            has_velocity = True
+        nqpoints = bands["nqpoint"][0]
+    assert has_eigenvectors and has_velocity
+    assert nqpoints == 306
+
+
+def test_force_consts_to_hdf5_deprecated(tmp_path):
+    """Test saving force constants to HDF5 deprecated."""
+    file_prefix = tmp_path / "test" / "NaCl"
+    phonon_results = tmp_path / "test" / "NaCl-phonopy.yml"
+    hdf5_results = tmp_path / "test" / "NaCl-force_constants.hdf5"
+    bands_results = tmp_path / "test" / "NaCl-auto_bands.hdf5"
+    summary_path = tmp_path / "test" / "NaCl-phonons-summary.yml"
+    log_path = tmp_path / "test" / "NaCl-phonons-log.yml"
+
+    result = runner.invoke(
+        app,
+        [
+            "phonons",
+            "--struct",
+            DATA_PATH / "NaCl.cif",
+            "--arch",
+            "mace_mp",
+            "--bands",
+            "--file-prefix",
+            file_prefix,
+            "--force-consts-to-hdf5",
+        ],
+    )
+
+    assert result.exit_code == 0
+    assert phonon_results.exists()
+    assert hdf5_results.exists()
+    assert bands_results.exists()
 
     # Read phonons summary file
     with open(summary_path, encoding="utf8") as file:
@@ -180,7 +243,7 @@ def test_hdf5(tmp_path):
     output_files = {
         "params": phonon_results,
         "force_constants": hdf5_results,
-        "bands": None,
+        "bands": bands_results,
         "bands_plot": None,
         "dos": None,
         "dos_plot": None,
@@ -289,10 +352,10 @@ def test_plot(tmp_path):
     """Test for plotting routines."""
     file_prefix = tmp_path / "NaCl"
     phonon_results = tmp_path / "NaCl-phonopy.yml"
-    bands_path = tmp_path / "NaCl-auto_bands.yml.xz"
+    bands_path = tmp_path / "NaCl-auto_bands.yml"
     pdos_results = tmp_path / "NaCl-pdos.dat"
     dos_results = tmp_path / "NaCl-dos.dat"
-    autoband_results = tmp_path / "NaCl-auto_bands.yml.xz"
+    autoband_results = tmp_path / "NaCl-auto_bands.yml"
     summary_path = tmp_path / "NaCl-phonons-summary.yml"
     log_path = tmp_path / "NaCl-phonons-log.yml"
     svgs = [
@@ -630,7 +693,7 @@ def test_paths(tmp_path):
     """Test passing qpoint file."""
     file_prefix = tmp_path / "NaCl"
     qpoint_file = DATA_PATH / "paths.yml"
-    band_results = tmp_path / "NaCl-bands.yml.xz"
+    band_results = tmp_path / "NaCl-bands.yml"
 
     result = runner.invoke(
         app,
@@ -651,7 +714,7 @@ def test_paths(tmp_path):
     assert result.exit_code == 0
 
     assert band_results.exists()
-    with lzma.open(band_results, mode="rb") as file:
+    with open(band_results, encoding="utf-8") as file:
         bands = yaml.safe_load(file)
     assert bands["nqpoint"] == 11
     assert bands["npath"] == 1